Insulation and fault monitoring for enhanced fault detection

ABSTRACT

A fault monitoring device may monitor and detect for faults corresponding to a high-side voltage rail, to low-side voltage rail, or internally within a voltage source connected to the high-side voltage rail and the low-side voltage rail. The fault monitoring device may determine sample voltage levels and/or sample resistance values to detect the faults. Also, in various embodiments, the fault monitoring device may perform one or more fault monitoring processes over multiple stages. The fault monitoring device may determine the sample voltage levels and/or the sample resistance values while switching a secondary resistance circuit in different states over the multiple stages.

TECHNICAL FIELD

This disclosure relates to fault monitoring and, in particular, to faultmonitoring in connection with high-side and low-side insulationresistances in a high voltage bus.

BACKGROUND

Healthy power systems have large insulation resistance (e.g. >1 MΩ)between a high voltage bus having positive and negative voltage railsand ground. A breakdown in the insulation resistance due to a fault canlead to a short circuit between the high voltage bus and ground, loss ofthe bus, and equipment damage. Power systems are often connected toinsulation monitoring devices to detect faults in order to guard againstsuch damage. Existing insulation monitoring devices collectively monitorthe insulation resistance between both positive and negative rails tochassis, and monitor the insulation resistance only in its currentstate, not over time.

Initially, a fault to chassis may not cause a complete short circuit,but may develop into a full short circuit over time. Often times, suchinitial faults are internal to the power system loads or sources, ratherthan within the distribution system. Existing insulation monitoringdevices may not detect these internal faults. Consequently, suchinternal faults are latent faults that go undetected, and it is notuntil a full short circuit develops and equipment damage occurs that thefaults are detected. On the other hand, if an insulation monitoringdevice can detect such internal faults, short circuits and equipmentdamage could be avoided. As such, ways to improve insulation monitoringtechniques that allow for early detection of internal faults aredesirable, especially for safety critical applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale. Moreover, in the figures, like-referenced numeralsdesignate corresponding parts throughout the different views.

FIG. 1 shows a block diagram of a power system including a high voltagebus connected to an insulation monitoring device

FIG. 2 shows a flow chart of an example method of performing aninsulation resistance calculation process.

FIG. 3 . shows a flow chart of an example method of performing a faultmonitoring process to monitor for a high-level rail fault.

FIG. 4 shows a flow chart of an example method of performing a faultmonitoring process to monitor for a mid-level rail fault.

FIG. 5 shows a flow chart of an example method of performing a faultmonitoring process to monitor for a combination of a high-level railfault and a mid-level rail fault.

FIG. 6 shows a flow chart of an example method of performing a faultmonitoring process to monitor for an internal fault.

FIG. 7 shows a flow chart of an example method of performing a faultmonitoring process to monitor for an internal fault in combination withat least one of a high-level rail fault or a mid-level rail fault.

DETAILED DESCRIPTION

The present description describes apparatuses, devices, systems, andmethods for insulation monitoring and fault detection for high voltagebuses in power systems, such as power systems for vehicles, includingaircraft. The insulation monitoring described herein may measurevoltages levels on high-side and low-side voltage rails of the highvoltage bus, and determine or calculate resistance values for high-sideand low-side insulation resistances based on the measured voltages.Based on the resistance values, the insulation monitoring may detectwhether a fault is present between the high-side voltage rail and groundand/or between the low-side voltage rail and ground, and/or whether sucha fault is imminent. In addition or alternatively, the insulationmonitoring may determine whether an internal fault (a fault between aninternal location of a voltage source and ground) is present based onthe measured voltages. Such insulation monitoring may allow for earlydetection before a fault causes equipment failure. Other insulatingmonitoring techniques that determine a collective resistance value forthe high-side and low-side insulation resistances, rather thanindividual resistance values, may not be able to achieve or perform suchfault detection. Additionally, the detection provided by the insulationmonitoring described herein may assist with diagnostic and repair, whichin turn may lead to faster repair time. Additionally, the detectionprovided by the insulation monitoring described herein may be used forpredictive maintenance and insulation health prognostics, which in turnmay lead to cost savings to an operator.

In further detail, FIG. 1 shows a power system 100 (e.g., a directcurrent (DC) power system) that includes a high voltage bus 102 coupledto a fault monitoring device or circuit 104 (also referred to as aninsulation monitoring device in various embodiments). In variousembodiments, the power system 100 may implemented in a vehicle, such asan aircraft, an automobile, a train, or a water vessel, as non-limitingexamples. In addition or alternatively, in various embodiments, thepower system 100 may be an electric drive system (e.g., a hybridelectric drive system) for the overall system (e.g., the vehicle) inwhich it is implemented.

The high voltage bus 102 includes a high-side voltage rail 106 at whicha positive rail voltage PRV is generated with reference to a groundreference GND, and a low-side voltage rail 108 at which a negative railvoltage NRV is generated with reference to the ground reference GND. Invarious embodiments, both the positive rail voltage PRV and the negativerail voltage NRV are “high voltages” in that they both have largevoltage magnitudes, such as greater than 100 V. In one particularembodiment, the positive rail voltage PRV is +540 V and the negativerail voltage NRV is −540 V, although various other voltage values forthe positive rail voltage PRV and the negative rail voltage NRV may bepossible.

In addition, the power system 100 may include or at least be coupled toa voltage source 110 configured to generate the positive rail voltagePRV on the high-side voltage rail 106 and the negative rail voltage NRVon the low-side voltage rail 108. The voltage source 110 may beconsidered a component of the high voltage bus 102, or may be considereda component separate from the high voltage bus 102 to which the highvoltage bus 102 is coupled. Also, in various embodiments, the voltagesource 110 is a DC voltage source configured to generate the positiverail voltage PRV and the negative rail voltage NRV each as DC voltages.In addition or alternatively, the voltage source 110 may include of abattery pack, an electrical generator coupled with an AC/DC converterstage, a fuel cell, or any combination thereof. In addition, a DC/DCconverter used to regulate the bus voltage may or may not be included inthe power system 100. For at least some embodiments, such as shown inFIG. 1 , the battery pack has a plurality of battery cells 112 connectedin series with each other.

As shown in FIG. 1 , the voltage source 110 has a first end connected tothe high-side voltage rail 106 where the positive rail voltage PRV isgenerated, and a second end connected to the low-side voltage rail 108where the negative rail voltage NRV is generated. Portions of thevoltage source 110 other than the first and second ends may be internalportions of the voltage source 110. For example, where the voltagesource 110 is a battery including a plurality of series-connectedbattery cells 112, an internal portion may be where two battery cellsare connected to each other.

As described above, the high voltage bus 102 includes, or is coupled to,a ground GND. The voltage values of the positive rail voltage PRV andthe negative rail voltage NRV, and other voltage values of any othervoltage generated in the power system 100, may be with reference to theground GND. In various embodiments, including those where the powersystem is implemented in a vehicle, the ground GND may be a chassis ofthe vehicle.

The voltage bus 102 may have a high-side insulation resistance R_(IH)between the high-side voltage rail 106 and ground GND, and a low-sideinsulation resistance R_(IL) between the low-side voltage rail 108 andground GND. The high-side insulation resistance R_(IH) provideselectrical insulation between the high-side voltage rail 106 and groundGND. In addition, the low-side insulation resistance R_(IL) provideselectrical insulation between the low-side voltage rail 108 and groundGND. Also, for at least some embodiments, one or both of the high-sideinsulation resistance R_(IH) and the low-side insulation resistanceR_(IL) provides electrical insulation between the voltage source 110,including one or more internal locations of the voltage source 110(e.g., between two battery cells 112), and ground GND.

Optimally, each of the high-side and low-side insulation resistancesR_(IH), R_(IL) are relatively high, such as on the order of 1 MΩ orgreater, providing sufficient electrical insulation between thehigh-side voltage rail 106, the low-side voltage rail 108, and thevoltage source 110. However, during operation, one or both of thehigh-side and low-side insulation resistances R_(IH), R_(IL) maypartially or completely breakdown, lowering the amount of electricalinsulation they provide between ground GND and high-side voltage rail106, the low-side voltage rail 108, and/or the voltage source 110. Sucha breakdown or lowering of one or both of the insulation resistancesR_(IH), R_(IL) may create or produce a fault in the high voltage bus102.

In general, a fault is an unintended and/or abnormal flow of electricalcurrent from one point to another. In the high voltage bus 102, a faultcaused by a breakdown in the high and/or low insulation is most likelyto occur between ground GND and the high-side voltage rail 106, betweenground GND and the low-side voltage rail 108, and/or between ground GNDand an internal location within the voltage source 110, such as betweentwo battery cells 112. For clarity, as used herein, the term “railfault” and “internal fault” are used to distinguish between faultsbetween ground GND and the high-side and low-side voltage rails 106,108, and faults between ground GND and the voltage source 110 and/orinternal locations of the voltage source 110. Specifically, the term“rail fault” refers to a fault between the high-side voltage rail 106and ground GND or between the low-side voltage rail 108 and ground GND,and the term “internal fault” refers to a fault between the voltagesource 110 and ground GND and/or between an internal point or locationof the voltage source 110 (e.g., a connection point between two batterycells 112) and ground GND.

Not all faults are the same and some faults may be more critical orsevere than others. A fault that is highly severe or critical may causefailure of the high voltage bus 102, damage to the power system 100and/or the other components of the overall system (e.g., the vehicle),cause injury to people, and/or require immediate shutdown or attentionby an operator. Highly severe or critical faults may be caused by acomplete breakdown in one or both of the high-side and low-sideinsulation resistances R_(IH), R_(IL).

Other faults may be less than highly severe or critical. Suchless-severe faults may be caused by a less than a complete breakdown inone or both of the high-side and low-side insulation resistances R_(IH),R_(IL), may not cause system failure or damage, and/or may not requireimmediate attention. Nonetheless, these less-severe faults can turn intohighly severe faults if left unattended. As such, less-severe faultsshould be attended to in the near future (within a certain predeterminedtime period) to avoid these faults becoming highly severe faults thatcreate system failure or damage. In this regard, less-severe faults mayserve as a warning or a forecast that a highly severe fault is imminentif no further action is taken.

To further illustrate highly severe and less-severe faults, if a highlysevere fault is detected while a vehicle is in motion and/or in route toa destination, an operator may attend to the highly severe faultrelatively immediately, such as by shutting down and/or replacing one ormore components before the vehicle reaches its destination. On the otherhand, if a less-severe fault is detected while a vehicle is in motionand/or in route to a destination, an operator may attend to the lesssevere fault once the vehicle reaches its destination.

For clarity, the term “high-level fault” is used herein to refer to ahighly severe fault identified as causing system failure or damage,and/or identified as requiring immediate attention. Additionally, theterm “mid-level fault” is used herein to refer to a less-severe faultidentified as not causing system failure or damage, and/or identified asrequiring attention not immediately but in the near future (within acertain predetermined time period, such as within a certain number ofhours or days or upon arrival at a destination, as non-limitingexamples). The terms “high-level fault” and “mid-level fault” may beused alone, or may be used in combination with “rail” and “internal” toidentify both the severity of a fault and the type of fault in the highvoltage bus 102.

The fault monitoring device 104 is an electronic device that isconfigured to monitor for and detect faults, including rail faultsand/or internal faults, in the high voltage bus 102. To do so, the faultmonitoring device 104 may measure voltages corresponding to thehigh-side and low-side voltage rails 106, 108. In some embodiments, thefault monitoring device 104 may further determine or calculateresistance values for or corresponding to each of the high-side andlow-side insulation resistances R_(IH), R_(IL), and/or for orcorresponding to each of the high-side and low-side voltage rails 106,108, based on the measured voltages, and monitor for a rail fault basedon the calculated resistance values. In some of these embodiments, thefault monitoring device 104 may perform or execute a first faultmonitoring process based on at least one of the calculated the high-sideand/or low-side insulation resistance values to determine whether ahigh-level rail fault is present in the high voltage bus 102. In otherof these embodiments, the fault monitoring device 104 may perform orexecute a second fault monitoring process based on at least one of thecalculated resistance values to determine whether a mid-level rail faultis present in the high voltage bus 102.

In still other of these embodiments, the fault monitoring device 104 mayperform the first fault monitoring process and the second faultmonitoring process either in sequence or in parallel. When performingthe first and second fault monitoring processes in sequence, the faultmonitoring device 104 may perform one of the first fault monitoringprocess or the second fault monitoring process as an initial faultmonitoring process, and then may perform the other of the first andsecond fault monitoring processes as a subsequent fault monitoringprocess. In some embodiments, whether the fault monitoring device 104performs the subsequent fault monitoring process may depend on a faultresult of the initial fault monitoring process.

In other embodiments, the fault monitoring device 104 may perform athird fault monitoring process based on at least one of the measuredvoltages corresponding to the voltage rails 106, 108 to determinewhether an internal fault is present. In some embodiments, the faultmonitoring device 104 may perform the third fault monitoring process asa standalone fault detection process. In other embodiments, the faultmonitoring device 104 may perform the third fault monitoring process incombination at least one of the first or second fault monitoringprocesses. In some of these embodiments, the fault monitoring device 104may perform the third fault monitoring process, and determine whether toperform at least one of the first or second fault monitoring processesdependent on a fault result of the third fault monitoring process. Forexample, if the third fault monitoring process indicates that nointernal fault is present, then the fault monitoring device 104 mayperform at least one of the first or second fault monitoring processesto determine if a high-level and/or a mid-level rail fault is present.On the other hand, if the third fault monitoring process indicates thatan internal fault is present, then the fault monitoring device 104 maynot perform the first or second fault monitoring processes.

As described in further detail below, the fault monitoring device 104may perform at least one of the fault monitoring processes over aplurality of stages. In each stage, the fault monitoring device 104 maymeasure at least two voltage levels corresponding to at least one of thehigh-side voltage rail 106 or the low-side voltage rail 108, and/or toat least one of the high-side insulation resistance R_(IH) or thelow-side insulation resistance R_(IL). In addition, the fault monitoringdevice 104 may determine at least one fault result of the at least onefault monitoring process in at least one of the stages based on the atleast one measured voltage level.

Additionally, the fault monitoring device 104 includes a variableresistance circuit that is configured to variably connect to the highvoltage bus 102. In general, the variable resistance circuit includes anetwork or a plurality of resistance elements having a variableconnection to the high voltage bus 102. By having a variable connection,the number of resistance elements and/or which of the resistanceelements that connect to the high voltage bus 102 can change. Inaccordance with the variable connection, the variable resistance circuitcan be configured in a plurality of different states. In each state, thevariable resistance circuit has a certain configuration of theresistance elements connected to and disconnected from the high voltagebus 102. Different states have different configurations of theresistance elements connected to and disconnected from the high voltagebus 102.

As described in further detail below, the fault monitoring device 104can control the states of the variable resistance circuit over thestages of the at least one fault monitoring process. In particular, thefault monitoring device 104 may configure the variable resistancecircuit in different states over consecutive stages. In doing so, thefault monitoring device 104 has different configurations of resistanceelements connected to and disconnected from the high voltage bus 102over consecutive stages. As a result, the fault monitoring device 104measures voltage levels corresponding to the high-side and low-sidevoltage rails 106, 108 over the stages, with the voltage levels beingdependent on the different states of the resistance elements connectedto and disconnected from the high-side and low-side voltage rails 106,108 over these stages. The fault monitoring device 104 may then use thevoltage levels to determine at least one fault result for the at leastone fault monitoring process.

For at least some embodiments such as shown in FIG. 1 , the variableresistance circuit includes a primary resistance circuit 114 and asecondary resistance circuit 116, each configured to connect to the highvoltage bus 102. In the example embodiment shown in FIG. 1 , resistanceelements of the primary resistance circuit 114 include a high-sideprimary resistance R_(PH) and a low-side primary resistance R_(PL). Thehigh-side and low-side primary resistances R_(PH), R_(PL) may each beany discrete electrical component or element having an associatedelectrical resistance.

Each of the high-side primary resistance R_(PH) and the low-side primaryresistance R_(PL) are connected to the high voltage bus 102. By beingconnected to the high voltage bus 102, each of the high-side primaryresistance R_(PH) and the low-side primary resistance R_(PL) is able todraw current based on a voltage generated at the high-side voltage rail106 or the low-side voltage rail 108. In FIG. 1 , the high-side primaryresistance R_(PH) is connected to the high voltage bus 102 via thehigh-side voltage rail 106. The high-side primary resistance R_(PH) hasa first end connected to the high-side voltage rail 106 and a second endconnected to ground GND. Similarly, the low-side primary resistanceR_(PL) is connected to the high voltage bus 102 via the low-side voltagerail 108. The low-side primary resistance R_(PL) has a first endconnected to the low-side voltage rail 108 and a second end connected toground GND.

For some example embodiments such as shown in FIG. 1 , the primaryresistance circuit 114 is fixedly or always connected to the highvoltage bus 102. For other example embodiments, at least one of thehigh-side primary resistance R_(PH) or the low-side primary resistanceR_(PL), is variably or selectively connected to the high voltage bus102. By being variably selectively connected to the high voltage bus102, each of the high-side primary resistance R_(PH) and the low-sideprimary resistance R_(PL) can be configured to be electrically connectedto the high voltage bus 102 during some time periods of operation, andelectrically disconnected to the high voltage bus 102 during other timeperiods of operation. As mentioned, a resistance that is electricallyconnected to the high voltage bus 102 is able to draw current based on avoltage generated on the high-side voltage rail 106 or the low-sidevoltage rail 108. Conversely, a resistance is electrically disconnectedfrom the high voltage bus 102 if it is unable to draw current based on avoltage generated on the high-side voltage rail 106 or the low-sidevoltage rail 108.

For some example embodiments, the primary resistance circuit 114,including the high-side primary resistance R_(PH) and/or the low-sideprimary resistance R_(PL), is variably or selectively connected to thehigh voltage bus 102 via a set of one or more switches. As used herein,a switch is an electrical component that is configured to switch oralternate between two states, including an on or closed state, and anoff or open state. In the on state, the switch electrically connects twocomponents together by providing a path of low resistance between thetwo components. In particular embodiments, the low resistance issufficiently low, such that the switch in the on state effectivelyfunctions as a short circuit. In the off state, the switch electricallydisconnects two components by providing a path of high resistancebetween the two components. In particular embodiments, the highresistance is sufficiently high, such that the switch in the off stateeffectively functions as an open circuit.

For some embodiments where the high-side primary resistance R_(PH) isselectively connected to the high voltage bus 102, a switch iselectrically configured between the high-side primary resistance R_(PH)and the high-side voltage rail 106, selectively connecting the first endof the high-side primary resistance R_(PH) to the high-side voltage rail106. In other embodiments, a switch is electrically configured betweenthe high-side primary resistance R_(PH) and ground GND, selectivelyconnecting the second end of the high-side primary resistance R_(PH) toground GND. In still other embodiments, a first switch is electricallyconfigured between the high-side primary resistance R_(PH) and thehigh-side voltage rail 106, and a second switch is electricallyconfigured between the high-side primary resistance R_(PH) and groundGND. Various ways of selectively connecting the high-side primaryresistance R_(PH) to the high voltage bus 102 via the high-side voltagerail 106 using one or more switches may be possible.

Similarly, for some embodiments where the low-side primary resistanceR_(PL) is selectively connected to the high voltage bus 102, a switch iselectrically configured between the low-side primary resistance R_(PL)and the low-side voltage rail 108, selectively connecting the first endof the low-side primary resistance R_(PL) to the low-side voltage rail108. In other embodiments, a switch is electrically configured betweenthe low-side primary resistance R_(PL) and ground GND, selectivelyconnecting the second end of the low-side primary resistance R_(PL) toground GND. In still other embodiments, a first switch is electricallyconfigured between the low-side primary resistance R_(PL) and thelow-side voltage rail 108, and a second switch is electricallyconfigured between the low-side primary resistance R_(PL) and groundGND. Various ways of selectively connecting the low-side primaryresistance R_(PL) to the high voltage bus 102 via the low-side voltagerail 108 using one or more switches may be possible.

In addition, the secondary resistance circuit 116 of the variableresistance circuit is configured to selectively connect to the highvoltage bus 102. For at least some embodiments such as shown in FIG. 1 ,the variable resistance circuit is configured to change its variableconnection to the high voltage bus 102 through the secondary resistancecircuit 116. In the example embodiment shown in FIG. 1 , the resistanceelements of the secondary resistance circuit 116 include a high-sidesecondary resistance R_(SH) and a low-side secondary resistance R_(SL).The high and low-side secondary resistances R_(SH), R_(SL) may each beany discrete electrical component having an associated electricalresistance. By being selectively connected to the high voltage bus 102,each of the high-side secondary resistance R_(SH) and the low-sidesecondary resistance R_(SL) are configured to be electrically connectedto the high voltage bus 102 during some time periods of operation, andelectrically disconnected from the high voltage bus 102 during othertime periods of operation.

The high-side secondary resistance R_(SH) is electrically connected tothe high voltage bus 102 when it is able to draw current based on avoltage generated on the high-side voltage rail 106. For example, whenthe high-side secondary resistance R_(SH) is electrically connected tothe high voltage bus 102, the high-side secondary resistance R_(SH) isable to draw current from the high-side voltage rail 106 to ground GND.Conversely, when the high-side secondary resistance R_(SH) iselectrically disconnected from the high voltage bus 102, the high-sidesecondary resistance R_(SH) is unable to draw current based on a voltagegenerated on the high-side voltage rail 106. For example, when thehigh-side secondary resistance R_(SH) is electrically disconnected fromthe high voltage bus 102, the high-side secondary resistance R_(SH) isunable to draw current from the high-side voltage rail 106 to groundGND.

Similarly, the low-side secondary resistance R_(SL) is electricallyconnected to the high voltage bus 102 when it is able to draw currentbased on a voltage generated on the low-side voltage rail 108. Forexample, when the low-side secondary resistance R_(SL) is electricallyconnected to the high voltage bus 102, the low-side secondary resistanceR_(SL) is able to draw current from the low-side voltage rail 108 toground GND. Conversely, when the low-side secondary resistance R_(SL) iselectrically disconnected from the high voltage bus 102, the low-sidesecondary resistance R_(SL) is unable to draw current based on a voltagegenerated on the low-side voltage rail 108. For example, when thelow-side secondary resistance R_(SL) is electrically disconnected fromthe high voltage bus 102, the low-side secondary resistance R_(SL) isunable to draw current from the low-side voltage rail 108 to ground GND.

For at least some embodiments such as shown in FIG. 1 , the faultmonitoring device 104 further includes a switching circuit 118 that isconfigured to selectively connect the secondary switching circuit 116,including the high and low-side secondary resistances R_(SH), R_(SL), tothe high voltage bus 102. In the example embodiment shown in FIG. 1 ,the switching circuit 118 includes a first switch SW1 electricallyconfigured between the high-side secondary resistance R_(SH) and thehigh-side voltage rail 106, selectively connecting a first end of thehigh-side secondary resistance R_(SH) to the high-side voltage rail 106.For such embodiments, a second end of the high-side secondary resistanceR_(SH) is directly connected to ground GND. In other embodiments, thefirst switch SW1 is electrically configured between the high-sidesecondary resistance R_(SH) and ground GND, selectively connecting thesecond end of the high-side secondary resistance R_(SH) to ground GND.For such embodiments, the first end of the high-side secondaryresistance R_(SH) is directly connected to the high-side voltage rail106. In still other embodiments, the first switch SW1 includes twoswitches, one electrically configured between the high-side secondaryresistance R_(SH) and the high-side voltage rail 106, and a secondswitch configured between the high-side secondary resistance R_(SH) andground GND. Various ways of selectively connecting the high-sidesecondary resistance R_(SH) to the high voltage bus 102 via thehigh-side voltage rail 106 using one or more switches may be possible.

Additionally, for some embodiments such as shown in FIG. 1 , theswitching circuit 118 includes a second switch SW2 electricallyconfigured between the low-side secondary resistance R_(SL) and thelow-side voltage rail 108, selectively connecting a first end of thelow-side secondary resistance R_(SL) to the low-side voltage rail 108.For such embodiments, a second end of the low-side secondary resistanceR_(SL) is directly connected to ground GND. In other embodiments, thesecond switch SW2 is electrically configured between the low-sidesecondary resistance R_(SL) and ground GND, selectively connecting thesecond end of the low-side secondary resistance R_(SL) to ground GND.For such embodiments, the first end of the low-side secondary resistanceR_(SL) is directly connected to the low-side voltage rail 108. In stillother embodiments, the second switch SW2 includes two switches, oneelectrically configured between the low-side secondary resistance R_(SL)and the low-side voltage rail 108, and a second switch configuredbetween the low-side secondary resistance R_(SL) and ground GND. Variousways of selectively connecting the low-side secondary resistance R_(SL)to the high voltage bus 102 via the low-side voltage rail 108 using oneor more switches may be possible.

By configuring the secondary resistance circuit 116 to be selectivelyconnectable to the high voltage bus 102 via the switching circuit 118,the secondary resistance circuit 116 and/or the switching circuit 118are configurable in different states during different periods ofoperation. As used herein, a state identifies a particular combinationof the high-side secondary resistance R_(SH) being electricallyconnected to or disconnected from the high voltage bus 102, and thelow-side secondary resistance R_(SL) being electrically connected ordisconnected from the high voltage bus 102. In addition oralternatively, a state identifies a particular combination of the firstswitch SW1 in the on state or the off state, and the second switch SW2in the on state or the off state that configures the high and low-sidesecondary resistances R_(SH), R_(SL) in a particular combination ofbeing electrically connected to and disconnected from the high voltagebus 102. The variable resistance circuit is configured to change itsvariable connection to the high voltage bus 102 by configuring thesecondary resistance circuit 116 and/or the switching circuit 118 indifferent states during different periods of operation.

Additionally, different states have different combinations of the highand low-side secondary resistances R_(SH), R_(SL) being electricallyconnected to or disconnected from the high voltage bus 102, and/ordifferent combinations of the first and second switches SW1, SW2 in onand off states. As an example illustration, in a first state (State 0),both of the first and second switches SW1, SW2 are in off states, andcorrespondingly, both of the high and low-side secondary resistancesR_(SH), R_(SL) are electrically disconnected from the high voltage bus102. In a second state (State 1), the first switch SW1 is turned off andthe second switch SW2 is turned on, and correspondingly, the high-sidesecondary resistance R_(SH) is electrically disconnected from the highvoltage bus 102 and the low-side secondary resistance R_(SL) iselectrically connected to the high voltage bus 102. In a third state(State 2), both of the first and second switches SW1, SW2 are in onstates, and correspondingly, both of the high and low-side secondaryresistances R_(SH), R_(SL) are electrically connected to the highvoltage bus 102. In a fourth state (State 3), the first switch SW1 isturned on and the second switch SW2 is turned off, and correspondingly,the high-side secondary resistance R_(SH) is electrically connected tothe high voltage bus 102 and the low-side secondary resistance R_(SL) iselectrically disconnected from the high voltage bus 102.

In addition, the fault monitoring device 104 may include a high-sidevoltage measuring circuit 120 that is configured to measure a high-sidemeasurement voltage V_(MH) across the high-side primary resistanceR_(PH), and a low-side voltage measuring circuit 122 that is configuredto measure a low-side measurement voltage V_(ML) across the low-sideprimary resistance R_(PL). Since the high-side primary resistance R_(PH)is connected to the high-side voltage rail 106, then the high-sidemeasurement voltage V_(MH) may be considered to correspond to thehigh-side voltage rail 106, and the measured level (magnitude) of thehigh-side measurement voltage V_(MH) may be, or may otherwise beproportional to or indicate, the level of the positive rail voltage PRVrelative to ground GND. Similarly, since the low-side primary resistanceR_(PL) is connected to the low-side voltage rail 108, then the low-sidemeasurement voltage V_(ML) may be considered to correspond to thelow-side voltage rail 108, and the measured level (magnitude) of thelow-side measurement voltage V_(ML) may be, or may otherwise beproportional to or indicate, the level of the negative rail voltage NRV.

Further, the fault monitoring device 104 may include a controller 124that is configured to control one or more fault monitoring processesperformed by the fault monitoring device 104. The controller 124 isgenerally an electronic device or circuit, implemented in hardware, or acombination of hardware and software. In various embodiments, thecontroller 124 includes a processor and a memory. In general, theprocessor (or processor circuitry) is a component of the controller 124,implemented in hardware alone, or as a combination of hardware andsoftware, that is configured to perform any of various electronicfunctions described herein. In various embodiments where the controller124 uses software to perform or carry out a given function, the functionmay have associated computer code or a set of computer instructions,stored in at least a portion of the memory. The processor is configured,such as a microprocessor, a central processing unit (CPU), or the like,to access the memory and execute the computer code/instructions in orderto carry out the function. Also, in various embodiments the controller124 may use hardware only, such as in the form of digital logiccircuitry or the like, to perform a given function. Accordingly, in anyof various embodiments, to perform the functions described herein, theprocessor may use hardware circuitry only to perform functions, executecomputer software code/instructions stored in the memory to performfunctions, or a combination thereof. In various embodiment, thecontroller 124 may be or include an integrated circuit (IC), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), a circuit, a digital logic circuit, an analogcircuit, a combination of discrete circuits, gates, or any other type ofhardware or combination thereof. In addition, the memory may beimplemented according to any of various types of memory configured tostore electronic data, including volatile memory, non-volatile memory,combinations therefore, or any other types of memory configured to storedata, such in the form of digital bits of information. As mentioned, thememory may store computer code or instructions that the processor isconfigured to execute in order to carry out one or more of the functionsdescribed herein. For example, in various embodiment, the memory maystore computer-implemented algorithms, such as the alignment and localbest fit algorithms described herein. As another example, the memorystores software that the processor executes to establish a virtualworkspace and virtually move data, such as scan mesh data, in thevirtual workspace. In addition or alternatively, the memory isconfigured to store data, such as any of various voltage and/orresistance values the controller 124 determines or calculates.

To control at least one fault monitoring process, the controller 124 maydetermine states for the secondary resistance circuit 116 and theswitching circuit 118, and configure the first and second switches SW1,SW2 in respective on/off states corresponding to the determined states.In addition, the controller 124 may determine at least two voltagelevels of at least one of the high-side measurement voltage V_(MH) andthe low-side measurement voltage V_(ML), as measured or sensed by thehigh-side voltage measuring circuit 120 and the low-side voltagemeasuring circuit 122, respectively. Additionally, in some embodimentsas described in further detail below, the controller 124 may determineor calculate at least one sample resistance value corresponding to atleast one of the high-side insulation resistance R_(IH) and the low-sideinsulation resistance RI based on the at least two determined voltagelevels. Based on the at least two determined voltage levels and/or theat least one sample resistance value, the controller 124 may determine ahealth status of the high voltage bus 102, including whether or not ahigh-level rail fault, a mid-level rail fault, and/or an internal faultare present in the high voltage bus 102.

In addition, the controller 124 may perform at least one faultmonitoring process over a plurality of stages. Each stage may correspondto a respective one of the plurality of states that the secondaryresistance circuit 116 and/or the switching circuit 118 areconfigurable. To perform a current stage of a fault monitoring process,the controller 124 may determine a corresponding state for the secondaryresistance circuit 116 that corresponds to the current stage. In turn,the controller 124 may configure the secondary resistance circuit 116 inthe corresponding state, such as by configuring each of the first switchSW1 and the second switch SW2 in a respective on/off state thatcorresponds to the corresponding state, which in turn configures each ofthe high-side secondary resistance R_(SH) and the low-side secondaryresistance R_(SL) as being electrically connected to or disconnectedfrom the high voltage bus 102 corresponding to the corresponding state.With the secondary resistance circuit 116 and the switching circuit 118configured in the corresponding state, the controller 124 may determinea level of the high-side measurement voltage V_(MH) as measured orsensed by the high-side voltage measuring circuit 120 and a level of thelow-side measurement voltage V_(LH) as measured or sensed by thelow-side voltage measuring circuit 122 for the current stage. Inaddition, in some embodiments as described in further detail below, thecontroller 124 may determine or calculate resistance values for thehigh-side and low-side insulation resistance values R_(IH), R_(IL) forthe current stage based on the levels of the high-side and low-sidemeasurement voltages V_(MH), V_(ML) determined for the current stage.Upon determining the high-side and low-side measurement voltages V_(MH),V_(ML) for the current stage, the controller 124 may move on ortransition to a next stage of the fault monitoring process, whichbecomes the current stage, and may again proceed as described above.

For at least some embodiments, the controller 124 may perform at leastone fault monitoring process over the plurality of stages according to astate sequence. In general, a state sequence identifies a predeterminedsequence or order of the states in which the controller 124 configuresthe secondary switching circuit 116 and the switching circuit 118 overthe plurality of stages. The state sequence may identify a particularstate for a next stage relative to a state corresponding to a currentstage. Accordingly, when determining to perform a next stage of at leastone fault monitoring process, the controller 124 may determine acorresponding state for the next stage based on the state of the currentstage and the state sequence.

In one example embodiment, using the example states described above, thestate sequence may be State 0, State 1, State 2, and State 3 repeating.Accordingly, where the controller 124 configures the secondaryresistance and switching circuits 116, 118 in State 0 for a currentstage, the controller 124 configures the secondary resistance andswitching circuits 116, 118 in State 1 for a next stage, and thenconfigures the secondary resistance and switching circuits 116, 118 inState 2 for a third stage, and then configures the secondary resistanceand switching circuits in State 3 for a fourth stage. The controller 124may then reconfigure the secondary resistance and switching circuits116, 118 in State 0 for a fifth stage, and repeat.

In addition or alternatively, the controller 124 may perform at leastone fault monitoring process over a plurality of cycles. The number ofstages in a cycle may be equal to the number of different states, andeach stage in a cycle may correspond to a different one of the pluralityof states. Each cycle may have an associated state sequence or order,such as State 0, State 1, State 2, State 3, as a non-limiting example.For a current cycle, upon performing a last stage corresponding to alast state in the state sequence, the controller 124 may then transitionto a next cycle of the fault monitoring process. For example, afterperforming a last stage corresponding to State 3 of a current cycle, thecontroller 124 then performs a first stage corresponding to State 0 of anext cycle.

As shown in FIG. 1 , when the fault monitoring device 104 is connectedto the high voltage bus 102, the primary resistance circuit 114 isconnected in parallel with the insulation resistance. Specifically, thehigh-side primary resistance R_(PH) is connected in parallel with thehigh-side insulation resistance R_(IH), and the low-side primaryresistance R_(PL) is connected in parallel with the low-side insulationresistance R_(IL). As used herein, the term high-side parallelresistance connection refers to the parallel connection of the high-sideinsulation resistance R_(IH) and the high-side primary resistanceR_(PH), and the term low-side parallel resistance connection refers tothe parallel connection of the low-side insulation resistance R_(IL) andthe low-side primary resistance R_(PL).

In addition, the secondary resistance circuit 116 is configured toselectively connect to the high-side and low-side parallel resistanceconnections. In particular, when the high-side secondary resistanceR_(SH) is electrically connected to the high voltage bus 102, thehigh-side secondary resistance R_(SH) is connected in parallel with thehigh-side parallel resistance connection. Conversely, when the high-sidesecondary resistance R_(SH) is electrically disconnected from the highvoltage bus 102, the high-side secondary resistance R_(SH) is notconnected in parallel with the high-side parallel resistance connection.Likewise, when the low-side secondary resistance R_(SL) is electricallyconnected to the high voltage bus 102, the low-side secondary resistanceR_(SL) is connected in parallel with the low-side parallel resistanceconnection. Conversely, when the low-side secondary resistance R_(SL) iselectrically disconnected from the high voltage bus 102, the low-sidesecondary resistance R_(SL) is not connected in parallel with thelow-side parallel resistance connection.

By being configured to selectively connect the secondary resistancecircuit 116 to the high voltage bus 102, the controller 124 isconfigured to change the variable connection of the variable resistancecircuit to the high voltage bus 102 during a fault monitoring process.In particular, the controller 124 is configured to add or injectdifferent combinations of the high and low-side secondary resistancesR_(SH), R_(SL) to the high-side and low-side parallel resistanceconnections, respectively, over different stages of the fault monitoringprocess. For example, using the states identified above, when thecontroller 124 performs a stage corresponding to State 0, the controller124 does not add or inject either the high-side secondary resistanceR_(SH) to the high-side parallel resistance connection or the low-sidesecondary resistance R_(SL) to the low-side parallel resistanceconnection. When the controller 124 performs a stage corresponding toState 1, the controller 124 connects in parallel the low-side secondaryresistance R_(SL) to the low-side parallel resistance connection,without connecting in parallel the high-side secondary resistance R_(SH)to the high-side parallel resistance connection. When the controllerperforms a stage corresponding to State 2, the controller 124 bothconnects the high-side secondary resistance R_(SH) in parallel with thehigh-side parallel resistance connection, and connects the low-sidesecondary resistance R_(SL) in parallel with the low-side parallelresistance connection. When the controller performs a stagecorresponding to State 3, the controller 124 connects the high-sidesecondary resistance R_(SH) in parallel with the high-side parallelresistance connection, without connecting in parallel the low-sidesecondary resistance R_(SL) to the low-side parallel resistanceconnection.

As mentioned, when the controller 124 performs a given stage of a faultmonitoring process, the controller 124 may determine a level of thehigh-side measurement voltage V_(MH) across the high-side primaryresistance R_(PH) and a level of the low-side measurement voltage V_(ML)across the low-side primary resistance R_(PL) for the given stage. Inaddition, in some embodiments, the controller 124 may calculate sampleresistance values corresponding to the high-side and low-side insulationresistances R_(IH), R_(IL) based on the levels of the high-side andlow-side measurement voltages V_(MH), V_(ML) for the given stage. Asdescribed in further detail below, a sample resistance value may be, ormay otherwise indicate, correspond to, or be based on, a resistancevalue of at least one of the high-side insulation resistance R_(IH) orthe low-side insulation resistance R_(IL). For example, as described infurther detail below, a sample resistance value may be, or may be afunction of at least one of: a resistance value of the high-sideparallel resistance connection, a resistance value of the low-sideparallel resistance connection, a resistance value of the high-sideinsulation resistance R_(IH), or a resistance value of the low-sideinsulation resistance R_(IL).

Further, for at least some embodiments, for a given stage, thecontroller 124 is configured to determine resistance values for thehigh-side and low-side parallel resistance connections based on thelevels of the high-side and low-side measurement voltages V_(MH),V_(ML), and then determine the resistance values for the high-side andlow-side insulation resistances R_(IH), R_(IL) based on the resistancevalues of the high-side and low-side parallel resistance connections. Inparticular example embodiments, for a given current stage, thecontroller 124 determines the resistance values for the high-side andlow-side parallel resistance connections further based on levels of thehigh-side and low-side measurement voltages V_(MH), V_(ML) determinedfrom the prior (i.e., directly or immediately prior) stage.

Additionally, in various embodiments, in some stages, the controller 124may first determine a resistance value for the high-side parallelresistance connection, and then determine a resistance value for thelow-side parallel resistance connection based on the resistance for thehigh-side parallel resistance connection. For other stages, thecontroller 124 may first determine a resistance value for the low-sideparallel resistance connection, and then determine a resistance valuefor the high-side parallel resistance connection based on the resistancevalue for the low-side parallel resistance connection.

In addition, in various embodiments, the controller 124 may beconfigured to determine resistance values for the high-side and low-sideparallel resistance connections, and/or the resistance values for thehigh-side and low-side insulation resistances R_(IH), R_(IL) accordingto one or more predetermined mathematical functions or formulas. Also,because the controller 124 adds or injects different combinations of thehigh and low-side secondary resistances R_(SH), R_(SL) to the high-sideand low-side parallel resistance connections according to differentstates in different stages, the resistance values for the low andhigh-side parallel resistance connections may be determined according todifferent mathematical formulas for stages corresponding to thedifferent states. Otherwise stated, the controller 124 may be configuredto use the same mathematical formulas for different stages thatcorrespond to the same state, and may use different mathematicalformulas for different stages that correspond to different states.

In particular embodiments where the controller 124 performs aninsulation monitoring process according to the four States identifiedabove, and over cycles with a state order of {State 0, State 1, State 2,State 3} in each cycle, the controller 124 may determine a resistancevalue R_(H) for the high-side parallel resistance connection and aresistance value R_(L) for each stage according to the followingmathematical formulas:

For a current stage corresponding to State 0:

$\begin{matrix}{R_{H} = \frac{R_{SL}\left( {{U_{{ML}3}U_{{MH}0}} - {U_{{ML}0}U_{{MH}3}}} \right)}{U_{{ML}0}U_{{MH}3}}} & (1)\end{matrix}$ $\begin{matrix}{R_{L} = \frac{U_{{ML}0}R_{H}}{U_{{MH}0}}} & (2)\end{matrix}$

where R_(H) is the resistance value for the high-side parallelresistance connection, R_(SL) is the resistance value for the low-sidesecondary resistance R_(SL), R_(L) is the resistance value for thelow-side parallel resistance connection, U_(ML3) is the voltage level ofthe low-side measurement voltage V_(ML) for the directly prior stagecorresponding to State 3, U_(MH0) is the voltage level of the high-sidemeasurement voltage V_(MH) for the current stage corresponding to State0, U_(ML0) is the voltage level of the low-side measurement voltageV_(ML) for the current stage corresponding to State 0, and U_(MH3) isthe voltage level of the high-side measurement voltage V_(MH) for thedirectly prior stage corresponding to State 3.

For a current stage corresponding to State 1:

$\begin{matrix}{R_{L} = \frac{R_{SL}\left( {{U_{{MH}1}U_{{ML}0}} - {U_{{MH}0}U_{{ML}1}}} \right)}{U_{{MH}0}U_{{ML}1}}} & (3)\end{matrix}$ $\begin{matrix}{R_{H} = \frac{U_{{MH}0}R_{L}}{U_{{ML}0}}} & (4)\end{matrix}$

where U_(MH1) is the voltage level of the high-side measurement voltageV_(MH) for the current stage corresponding to State 1, U_(ML0) is thevoltage level of the low-side measurement voltage V_(ML) for thedirectly prior stage corresponding to State 0, U_(MH0) is the voltagelevel of the high-side measurement voltage V_(MH) for the directly priorstage corresponding to State 0, and U_(ML1) is the voltage level of thelow-side measurement voltage V_(ML) for the current stage correspondingto State 1.

For a current stage corresponding to State 2:

$\begin{matrix}{R_{L} = \frac{R_{SL}\left( {{U_{{MH}1}U_{{ML}2}} - {U_{{ML}1}U_{{MH}2}}} \right)}{{U_{{MH}1}U_{{MH}2}} + {U_{{ML}1}U_{{MH}2}} - {U_{{MH}1}U_{{ML}2}}}} & (5)\end{matrix}$ $\begin{matrix}{R_{H} = \frac{R_{SL}R_{L}U_{{MH}1}}{{R_{L}U_{{ML}1}} + {R_{SL}U_{{ML}1}}}} & (6)\end{matrix}$

where U_(MH1) is the voltage level of the high-side measurement voltageV_(MH) for the directly prior stage corresponding to State 1, U_(ML2) isthe voltage level of the low-side measurement voltage V_(ML) for thecurrent stage corresponding to State 2, U_(ML1) is the voltage level ofthe low-side measurement voltage V_(ML) for the directly prior stagecorresponding to State 1, and U_(MH2) is the voltage level of thehigh-side measurement voltage V_(MH) for the current stage correspondingto State 2.

For a current stage corresponding to State 3:

$\begin{matrix}{R_{H} = \frac{R_{SL}\left( {{U_{{MH}2}U_{{ML}3}} - {U_{{ML}2}U_{{MH}3}}} \right)}{{U_{{ML}2}U_{{MH}3}} + {U_{{ML}2}U_{{ML}3}} - {U_{{MH}2}U_{{ML}3}}}} & (7)\end{matrix}$ $\begin{matrix}{R_{L} = \frac{R_{SL}R_{H}U_{{ML}3}}{{R_{H}U_{{MH}3}} + {R_{SL}U_{{MH}3}}}} & (8)\end{matrix}$

where U_(MH2) is the voltage level of the high-side measurement voltageV_(MH) for the directly prior stage corresponding to State 2, U_(ML3) isthe voltage level of the low-side measurement voltage V_(ML) for thecurrent stage corresponding to State 3, U_(ML2) is the voltage level ofthe low-side measurement voltage V_(ML) for the directly prior stagecorresponding to State 2, and U_(MH3) is the voltage level of thehigh-side measurement voltage V_(MH) for the current stage correspondingto State 3.

For a given stage, upon determining a pair of resistance values R_(H),R_(L) for the high-side and low-side parallel resistance connections,the controller 124 may determine a pair of resistance values for thehigh-side and low-side insulation resistances R_(IH), R_(IL) based onthe pair of resistance values R_(H), R_(L) for the given stage accordingto the following mathematical formulas:

$\begin{matrix}{R_{IH} = \frac{R_{H}R_{SL}}{R_{SL} - R_{H}}} & (9)\end{matrix}$ $\begin{matrix}{R_{IL} = \frac{R_{L}R_{SL}}{R_{SL} - R_{L}}} & (10)\end{matrix}$

The above mathematical formulas (1)-(10) may be used by the controller124 where the resistance values for the high and low-side primary andsecondary resistance values R_(PH), R_(PL), R_(SH), R_(SL) are the same.Additionally, for the above mathematical formulas (1)-(10), the voltagelevels of the high-side and low-side measurement voltages V_(MH), V_(ML)are positive values, irrespective of whether the high-side and low-sidevoltage measuring circuit 120, 122 measure them as positive or negativevalues. For example, if the low-side voltage measuring circuit 122measures the low-side measurement V_(ML) as a negative value, the levelused for mathematical formulas (1)-(10) is an absolute value of thenegative value determined by the low-side voltage measuring circuit 122.Variations of the above mathematical formulas (1)-(10), including thosethat use negative versions of the voltage levels.

In various embodiments, because the controller 124 determines resistancevalues for the high-side and low-side insulation resistances R_(IH),R_(IL) for a current stage based on levels of the high-side and low-sidemeasurement voltages V_(MH), V_(ML) for the current stage and thedirectly prior stage, the controller 124, at a minimum, may perform afault monitoring process over a plurality of stages that corresponds toonly two states. For example, the controller 124 may perform a faultmonitoring process over a plurality of cycles, where each cycle includesthe same two states, such as {State 0, State 1}, {State 1, State 2},{State 2, State 3}, or {State 3, State 0}. In other embodiments, thecontroller 124 may perform a fault monitoring process over a pluralityof stages that corresponds to more than two states, such as three statesor four states. For example, the controller 124 may perform a faultmonitoring process over a plurality cycles, where each cycle includesthe same three states, such as {State 0, State 1, State 2}, {State 1,State 2, State 3}, {State 2, State 3, State 0}, or {State 3, State 0,State 1}. As another example, the controller 124 may perform a faultmonitoring process over a plurality of cycles, where each cycle includesthe same four states: {State 0, State 1, State 2, State 3}.

As mentioned, the fault monitoring device 104, is configured to performat least one fault monitoring process. Three fault monitoring processesare described herein. A first fault monitoring process monitors forhigh-level rail faults, a second fault monitoring process monitors formid-level rail faults, and a third fault monitoring process monitors forinternal faults, as those faults are described above. For each faultmonitoring process, the fault monitoring device 104 may determine anassociated fault result, which indicates whether or not the faultmonitoring device 104 has detected a fault corresponding to the faultmonitoring process. In various embodiments, the fault monitoring device104 may perform only one, only two, or all three of the fault monitoringprocesses. Also, in various embodiments, whether the fault monitoringdevice 104 performs, or at least determines a fault result of, one ormore of the fault monitoring processes may depend on a fault resultdetermined from performing another of the fault monitoring processes.Further, for embodiments where the fault monitoring device 104 performsmultiple fault monitoring processes, the processes may be consideredsub-processes of an overall fault monitoring process.

In addition, the fault monitoring device 104 may perform a single faultmonitoring process, or a combination of two or more fault monitoringprocesses, over multiple stages, as previously described. Within a givenstage, the controller 124 may configure the secondary resistance circuit116 in a state corresponding to the given stage, and with the secondaryresistance circuit 116 configured in that state, determine at least twovoltage levels of at least one of the high-side measurement voltageV_(MH) measured by the high-side voltage measuring circuit 120 or thelow-side measurement voltage V_(ML) measured by the low-side voltagemeasuring circuit 122.

For embodiments where the fault monitoring device 104 performs the firstfault monitoring process to determine whether a high-level rail fault ispresent, the controller 124 may further determine a pair of sampleresistance values based on the voltage measurements, including a firstsample resistance value corresponding to the high-side insulationresistance R_(IH) a second sample resistance value corresponding to thelow-side insulation resistance R_(IL). In various embodiments, the firstsample resistance value is, or is a function of, the high-sideinsulation resistance R_(IH) and/or the high-side parallel resistanceconnection R_(H), and the second sample resistance value is, or is afunction of, the low-side insulation resistance R_(IL) and/or thelow-side parallel resistance connection R_(L), such as determinedaccording to equations (1)-(10). For at least one of the stages, thecontroller 124 may compare the first sample resistance value with afirst threshold, and based on the comparison, determine whether ahigh-level rail fault is present between the high-side voltage rail 106and ground GND. For example, if the comparison indicates that the firstsample voltage is above the first threshold, then the controller 124 maydetermine that no high-level rail fault is present between the high-sidevoltage rail 106 and ground GND; and if the comparison indicates thatthe first sample voltage is below the first threshold, then thecontroller 124 may determine that a high-level rail fault is presentbetween the high-side voltage rail 106 and ground GND. In addition oralternatively, the controller 124 may compare the second sampleresistance value with a second threshold, and based on the comparison,determine whether a high-level rail fault is present between thelow-side voltage rail 108 and ground GND. For example, if the comparisonindicates that the second sample voltage is above the second threshold,then the controller 124 may determine that no high-level rail fault ispresent between the low-side voltage rail 108 and ground GND; and if thecomparison indicates that the second sample voltage is below the secondthreshold, then the controller 124 may determine that a high-level railfault is present between the low-side voltage rail 108 and ground GND.In various embodiments, the first and second thresholds may be the sameas or different than each other.

By performing two comparisons with the first and second sampleresistance values, the controller 124 may determine not only if ahigh-level rail fault is present in the high voltage bus 102, but also alocation of the high-level fault if one is present, including a locationbetween the high-side voltage rail 106 and ground GND or a locationbetween the low-side voltage rail 108 and ground GND. The controller 124identifying a location of the high-level fault may facilitate anoperator who is immediately attending to the high-level fault.

Also, in some embodiments where the first fault monitoring process isperformed, the controller 124 may perform the comparisons and/ordetermine a fault result in each stage. In other embodiments, thecontroller 124 may perform the comparisons and/or determine a faultresult in less than all of the stages. For example, the controller 124may perform the comparisons and determine fault results every Nth stage(where N is an integer of two or more). As another example, thecontroller 124 may perform the comparisons and determine fault resultsat certain predetermined time intervals. For example, when performing acurrent stage, then controller 124 may check whether a predeterminedtime period has elapsed. If not, then the controller 124 may move on toa next stage without performing any comparisons and/or determining anyfault results. Alternatively, if the controller 124 determines that atime period has elapsed, then the controller 124 may perform thecomparisons and/or determine fault results for the current stage.

In addition, for embodiments where the fault monitoring device 104performs the second fault monitoring process, the controller 124 maydetermine at least one sample resistance value, and perform at least onecomparison between the at least one sample resistance value and at leastone threshold. The controller 124 may determine the at least one sampleresistance value based on at least one of the measured voltage levels.The at least one sample resistance value may be different and/ordetermined differently than the first and second sample resistancevalues determined when performing the first fault monitoring process,and/or the at least one threshold used in second fault monitoringprocess may be different than the first and second thresholds used inthe first fault monitoring process.

In further detail, a sample resistance value used for the second faultmonitoring process may be based on, or associated with, the calculatedresistance values for the high-side and low-side insulation resistancesR_(IH), R_(IL) to detect a fault and/or a location of the fault. Invarious embodiments, the sample resistance value may be, or may be afunction of, at least one of: one or more resistance values of thehigh-side parallel resistance connection R_(H) for one or more stages,one or more resistance values of the low-side parallel resistanceconnection R_(L) for one or more stages, one or more resistance valuesof the high-side insulation resistance R_(IH) for one or more stages,one or more resistance values of the low-side insulation resistanceR_(IL) for one or more stages, or any of various combinations (e.g.,sums, differences, or averages as non-limiting examples) thereof.

In further examples, a sample resistance value used for the second faultmonitoring process may be, or may be a function of: a resistance valueof the high-side parallel resistance connection R_(H) for a singlestage; a combination (e.g., a sum or an average) of multiple resistancevalues of the high-side parallel resistance connection R_(H) formultiple stages; a resistance value of the low-side parallel resistanceconnection R_(L) for a single stage; a combination (e.g., a sum or anaverage) of multiple resistance values of the low-side parallelresistance connection R_(L) for multiple stages; a combination (e.g., adifference or an absolute value of a difference) of at least oneresistance value (e.g., a single resistance value for a single stage ormultiple resistance values for multiple stages) of the high-sideparallel resistance connection R_(H) and at least one resistance value(e.g., a single resistance value for a single stage or multipleresistance values for multiple stages); a resistance value of thehigh-side insulation resistance R_(IH) for a single stage; a combination(e.g., a sum or an average) of multiple resistance values of thehigh-side insulation resistance R_(IH) for multiple stages; a resistancevalue of the low-side insulation resistance R_(IL) for a single stage; acombination (e.g., a sum or an average) of multiple resistance values ofthe low-side insulation resistance R_(IL) for multiple stages; or acombination (e.g., a difference or an absolute value of a difference) ofat least one resistance value (e.g., a single resistance value for asingle stage or multiple resistance values for multiple stages) of thehigh-side insulation resistance R_(IH) and at least one resistance value(e.g., a single resistance value for a single stage or multipleresistance values for multiple stages) of the low-side insulationresistance R_(IL).

Additionally, for at least some example embodiments where a sampleresistance value used for the second fault monitoring process is, or isa function of, a combination of multiple resistance values, the multipleresistance values may be those that are for a current stage and a numberof directly prior stages, or a number of directly prior stages. Thenumber may be a predetermined integer, or may be a number of stagesoccurring with a predetermined time period or time window (e.g., apredetermined number of one or more hours or a predetermined number ofone or more days, as non-limiting examples) from a current stage or acurrent time identified by the controller 124. As an example, the sampleresistance value may be, or be a function of, a moving average ofresistance values determined from a predetermined number of lastperformed stages or from a number of stages performed within apredetermined time period or time window from a current time or currentstage.

In addition, in various embodiments, a sample resistance value for thesecond fault monitoring process may be a rate of change of a pluralityof resistance values. For example, the controller 124 may determine aplurality of resistance values for a number of last performed stages orfor a number of stages performed during a moving time window, and maydetermine a rate of change from the plurality of resistance values. Inparticular embodiments, the controller 124 may determine a rate ofchange based on a plurality of moving average values determined over themoving time window. For example, for each current stage, the controller124 may determine a new moving average value with a new sampleresistance value it determined from the current stage. The controller124 may then determine a new rate of change based on the updated movingaverage.

Additionally, in various embodiments where the second fault monitoringprocess is performed, the controller 124 may perform at least onecomparison that compares the at least one sample resistance value withat least one threshold. Based on the at least one comparison, thecontroller 124 may determine whether a mid-level rail fault is presentin the high voltage bus 102.

For some embodiments where the second fault monitoring process isperformed, the controller 124 may perform only a single comparison of asingle sample resistance value with a single threshold. In onenon-limiting example, the controller 124 may determine a sampleresistance value that is, or is a function of, a difference between afirst calculated resistance value corresponding to the high-side voltagerail 106 and a second calculated resistance value corresponding to thelow-side voltage rail 108, and compares the difference value with athreshold.

In other embodiments where the second fault monitoring process isperformed, the controller 124 may perform multiple comparisons, eachwith a respective one of multiple sample resistance values and arespective one of multiple thresholds. The controller 124 may determinethat a mid-level rail fault is present if at least one of thecomparisons so indicate. On the other hand, the controller 124 maydetermine that a mid-level fault is present is none of the comparisonsso indicate. As a non-limiting example of multiple comparisons performedfor the second fault monitoring process, the controller 124 may performa first comparison between a first sample resistance value and a firstthreshold, and may perform a second comparison between a second sampleresistance value and a second threshold, where the first sampleresistance value is a moving average of resistance values determinedfrom a predetermined number of last-performed stages or from stagesperformed over a last predetermined time period, and the second sampleresistance value is a rate of change of the resistance values. For thisexample, the first sample resistance value being below the firstthreshold may indicate that a mid-level rail fault is present, and thesecond sample resistance value being above the second threshold mayindicate that a mid-level rail fault is present.

Also, for some embodiments where the second fault monitoring process isperformed, the controller 124 may determine a difference between a firstsample resistance value corresponding to the high-side voltage rail 106and a second sample resistance value corresponding to the negativelow-side rail 108, as mentioned. For these embodiments, by determining adifference, the controller 124 may determine an amount of asymmetry orimbalance between the high-side and low-side insulation resistancesR_(IH), R_(IL). The amount of difference, asymmetry, or imbalance mayindicate a mid-level rail fault. That is, as long as the differencebetween the high-side and low-side insulation resistances R_(IH), R_(IL)is relatively small (below a threshold), then the controller 124 maydetermine that the high-side and low-side insulation resistances R_(IH),R_(IL) are healthy and no faults are imminent. On the other hand, if adifference is sufficiently large (above a threshold), then thecontroller 124 may determine that a mid-level rail fault is presentbetween.

Also, for at least some embodiments where the controller 124 performsthe second fault monitoring process by analyzing a difference (orimbalance or asymmetry) between the high-side and low-side insulationresistances R_(IH), R_(IL), the controller 124 may identify a polarityof the difference to determine a location of the mid-level fault,including a location between the high-side voltage rail 106 and groundGND or between the low-side voltage rail 108 and ground GND. Forexample, depending on how the difference is calculated, a polarity ofthe difference (positive or negative) may indicate which of theresistance values is higher than the other. If the controller 124determines that a magnitude of the difference is sufficiently large(above a threshold) such that a mid-level fault is present, then thecontroller 124 may determine a polarity of the difference to determinewhich of the insulation resistances R_(IH), R_(IL) is lower than theother. In turn, the controller 124 may determine the location of themid-level fault according to which of the insulation resistances R_(IH),R_(IL) is lower That is, if the polarity of the difference indicatesthat the high-side insulation resistance R_(IH) has the lower calculatedvalue, then the controller 124 may determine that the location of themid-level rail fault is between the high-side voltage rail 106 andground GND. On the other hand, if the polarity of the differenceindicates that the low-side insulation resistance R_(IL) has the lowercalculated value, then the controller 124 may determine that thelocation of the mid-level rail fault is between the low-side voltagerail 108 and ground GND.

In addition, for embodiments where the fault monitoring device 104performs the third fault monitoring process, the controller 124 maydetermine whether an internal fault, internal to the voltage source 110,is present based on voltage levels corresponding to at least one of thehigh-side voltage rail 106 or the low-side voltage rail 108 and for atleast two stages. The voltage levels may be, or may be determined from,at least one of the high-side measurement voltage V_(MH) or the low-sidemeasurement voltage V_(ML).

Accordingly, within a given stage, the controller 124 may determine asample voltage level, which may be, or may be a function of, a voltagelevel of the high-side measurement voltage V_(MH), a voltage level ofthe low-side measurement voltage V_(ML), or a combination of voltagelevels of the high-side and low-side measurement voltages V_(MH),V_(ML), such as a sum, difference, product, ratio, or any other form ofcombination of the two voltage levels. Further, for embodiments wherethe third fault monitoring process is performed, the controller 124 maydetermine a first sample voltage level for a current stage, anddetermine an amount of change between (such as by taking a differenceof) the first sample voltage level with a second sample voltage leveldetermined for a last (immediately prior) stage.

Further, the controller 124 may perform at least one comparison of atleast one amount of change with at least one threshold. The at least onecomparison indicates whether at least one of the high-side voltage rail106 or the low-side voltage rail 108 has changed above a threshold levelbetween a current stage and the prior stage. If it has, then the atleast one comparison may indicate that no internal fault is present.Alternatively, if it has not, then the at least one comparison mayindicate that an internal fault is present. In further detail, if nointernal fault is present, the changing of states in the secondaryresistance circuit 116 from one stage to the next may cause the voltagelevel of the positive rail voltage PRV to change a threshold amount, maycause the voltage level of the high-side measurement voltage V_(MH) tochange a threshold amount, may cause the voltage level of the negativerail voltage NRV to change a threshold amount, and/or may cause thevoltage level of the low-side measurement voltage V_(ML) to change athreshold amount. On the other hand, if an internal fault is present,the changing of states in the secondary resistance circuit 116 from acurrent stage to a next stage may not cause the voltage level changesabove a threshold amount. Accordingly, by detecting whether a samplevoltage level has changed above a threshold amount between twoconsecutive stages, the controller 124 may determine whether an internalfault is present.

Additionally, in various embodiments where the third fault monitoringprocess is performed, the controller 124 may perform at least onecomparison that compares at least one voltage level change with at leastone threshold. Based on the at least one comparison, the controller 124may determine whether an internal fault is present. In some embodiments,the controller 124 may determine a single sample voltage level in eachstage for the third fault monitoring process. For these embodiments, ina current stage, the controller 124 may determine an amount of change(such as a difference between) a current sample voltage level for thecurrent stage and a prior sample voltage level for the prior stage, andthen compare the amount of change with a threshold to determine if aninternal fault is present.

In other embodiments, the controller 124 may determine multiple samplevoltage levels in each stage for the third fault monitoring process,such as a first sample voltage level corresponding to the high-sidevoltage rail 106 and a second sample voltage level corresponding to thelow-side voltage rail 108. For these embodiments, in a current stage,the controller 124 may determine a first amount change between a currentfirst sample voltage level a prior first sample voltage corresponding tothe high-side voltage rail 106, and/or a second amount of change betweena current second sample voltage level and a prior second sample voltagelevel corresponding to the low-side voltage rail 108. The controller 124may perform a first comparison between the first amount of change and athreshold, and a second comparison between the second amount of changeand the threshold, to determine whether an internal fault is present. Insome embodiments, the controller 124 may perform the comparisons insequence. The controller 124 may perform one of the first and secondcomparisons as an initial comparison, and then perform the other of thefirst and second comparisons as a subsequent comparison. In variousembodiments, whether the controller 124 performs the subsequentcomparison may depend on a comparison result of the initial comparison.For example, the controller 124 may perform the subsequent comparisononly if the initial comparison indicates an internal fault is present,and determines an internal fault is present only if both comparisonsindicate that the internal fault is present. As another example, thecontroller 124 may perform the subsequent comparison only if the initialcomparison indicates an internal fault is not present. That is, if theinitial comparison indicates that an internal fault is present, thecontroller 124 determines that an initial fault is present withoutperforming the sequent comparison. However, if the initial comparisonindicates that an internal fault is not present, then the controller 124performs the subsequent comparison, and determines that an internalfault is present if the subsequent comparison indicates that an internalfault is present. Accordingly, for this example, controller 124determines that an internal fault is present if at least one of theinitial and subsequent comparisons indicates that an internal fault ispresent, and determines that an internal fault is not present only ifneither of the comparisons indicate that an internal fault is notpresent. In other of various embodiments, the controller 124 alwaysperforms both comparisons, and determines an internal fault is presentonly if both comparisons indicate that the internal fault is present. Ifat least one of the comparisons indicates that an internal fault is notpresent, then the controller 124 determines that an internal fault isnot present.

In addition, in some embodiments of the third fault monitoring process,in response to determining that an internal fault is present, thecontroller 124 may further determine an internal location of theinternal fault. An internal location of an internal fault may be orindicate a location or point, such as a connection point, that theinternal fault is between and ground GND. As mentioned, an internallocation of the voltage source 110 may be a point between two batterycells. Accordingly, in some embodiments of the third fault monitoringprocess, by determining an internal location of an internal fault, thecontroller 124 identifies a point between two battery cells 112, among aplurality of different points between different battery cells within thevoltage source 110. The controller 124 may identify the point byidentifying two battery cells that the point is between.

Also, the controller 124 may determine an internal location based on thesample voltage levels, including a first sample voltage levelcorresponding to the high-side voltage rail 106 and a second samplevoltage level corresponding to the low-side voltage rail 108. Inparticular embodiments, the controller 124 may determine a ratio betweenthe first sample voltage level and the second sample voltage level,which in turn may be equal or proportional to a ratio of a number ofbattery cells 112 between the internal fault location and the high-sidevoltage rail 106 and a number of battery cells 112 between the internalfault location and the low-side voltage rail 108.

As an example illustration, suppose the voltage source 110 has tenbattery cells 112, with each battery cell 112 having 1 V. Further,suppose that over two stages, including a prior stage and a currentstage, the controller 124 determines a magnitude of the negative railvoltage NRV to be effectively constant at 4 V (i.e., a change inmagnitude of the negative rail voltage NRV between the prior and currentstages is below a threshold level), and a magnitude of the positive railvoltage PRV to be effectively constant at 6 V (i.e., a change inmagnitude of the positive rail voltage PRV between the prior and currentstages is below a threshold level), yielding a PRV-to-NRV ratio of 6 to4. In turn, the ratio may indicate to the controller 124 that theinternal fault location is six battery cells from the high-side voltagerail 106 and four battery cells from the low-side voltage rail 108, orbetween the fourth and fifth battery cells. As another example, supposethat over two stages, including a prior stage and a current stage, thecontroller 124 determines a magnitude of the negative rail voltage NRVto be effectively constant at 3 V (i.e., a change in magnitude of thenegative rail voltage NRV between the prior and current stages is belowa threshold level) and a magnitude of the positive rail voltage to beeffectively constant at 7 V (i.e., a change in magnitude of the positiverail voltage PRV between the prior and current stages is below athreshold level), yielding a PRV-to-NRV ratio of 7 to 3. In turn, theratio may indicate to the controller 124 that the internal faultlocation is seven battery cells from the high-side voltage rail 106 andthree battery cells from the low-side voltage rail 108, or between thethird and fourth battery cells.

In addition or alternatively, in any of various embodiments, thecontroller 124 may save the any of the various voltage levels and/orcalculated resistance values for the plurality of stages over time, suchas historical data. As described in further detail below, the historicaldata may be used to track how the high-side and low-side insulationresistances R_(IH), R_(IL) change over time, either internally by thecontroller 124, or by an operator, such as by viewing the historicaldata on a display. The historical data may be used for predictivemaintenance by providing data that can be used, either internally by thecontroller 124 or by an operator receiving the data, for insulationhealth prognostics, which in turn can provide cost savings.

Further, in various embodiments such as shown in FIG. 1 , the system 100may include an output device 126 in electrical communication with thecontroller 124. The output device 126 may be any device configured tooutput an output signal associated with at least one fault monitoringprocess. The output signal may be in the form of at least one of: audiosignals, video signals, or light signals associated with the at leastone fault monitoring process. In various embodiments, the output device126 may include at least one of a speaker, a display, or a light source.

In some embodiments, the output device 126 is a component of the faultmonitoring device 104. For example, the fault monitoring device 124itself may include a display, a speaker, and/or a light source. In otherembodiments, the output device 126 may be a component separate from thefault monitoring device 104. For these latter embodiments, thecontroller 124, and/or the fault monitoring device 104 as a whole, maybe configured to communicate with the separate output device 126 via anyof various wired and/or wireless electrical connections to communicateone or more signals to and/or from the output device 126 to cause theoutput device 126 to output any of various audio, video, and/or lightsignals. For example, in some embodiments, the fault monitoring device104 and the output device 126 may be configured to form and/or connectto one or more of any of various types of communication networks, suchas in accordance with any of various types of standards or protocols(e.g., a local area network, a wireless local area network, a wide areanetwork, a metropolitan area network, a cloud computing network, avirtual private network, a controller area network (CAN), a personalarea network, a cellular network, the Internet, as non-limitingexamples) and communicate with each other via the one or more networks.Accordingly, the actual output device 126 of the monitoring device 104may be in the form of any of various types of transmitter or transceivercircuitry, such as a connector, port, and/or antenna or antenna array,that is configured to wirelessly communicate (send and receive) signalsand/or connect to a wired connection (e.g., an Ethernet or a coaxialcable) or a communication bus (e.g., a CAN bus), for communication overthe one or more networks. In other embodiments, the fault monitoringdevice 104 may communicate with the output device 126 via a wired and/orwireless connection without connection to or use of a network. Variousways of configuring an output device 126 to be in electricalcommunication with the controller 124 of the fault monitoring device 104for output of one or more signals related to the fault monitoringperformed by the fault monitoring device 104 may be possible.

Additionally, in various embodiments, the output signal may indicate ahealth status of the power system 100. The health status may indicatewhether a fault is detected. If the controller 124 determines there areno faults from performing the at least one fault monitoring process, theoutput device 126 does not output anything, the silence or absence ofthe output signal indicating that the power system 100 is healthy, whichin turn may indicate to an operator that the power system 100 is notexperiencing any faults and no action is required. In other embodiments,the output signal may expressly indicate that no fault is detected. Forexample, the output device 126 may be in the form of a display thatdisplays text or another type of graphic indicating that no fault ispresent. As another example, the output device 126 may output a lightsignal a certain way (such as with a certain color, e.g., green)indicating that no fault has been detected.

In addition, if the controller 124 has detected a fault, the outputdevice 126 may output an output signal to indicate that a fault isdetected. Also, in various embodiments, the output signal may indicate atype of the detected fault, such as whether the fault is a high-levelrail fault, a mid-level rail fault, or an internal fault. In addition oralternatively, in various embodiments, the controller 124 may output theoutput signal to indicate a location of the fault, such as if the faultis between the high-side voltage rail 106 and ground GND, or between thelow-side voltage rail 108 and ground GND. The output device 126 mayoutput an output signal in any of various ways, audibly and/or visibly,to indicate the detected fault. For example, the output device 126 maybe a speaker that outputs an audio signal, such as in the form of analarm or a voice. In addition or alternatively, the output device 126may be a light source that output a light signal, such as a flashinglight signal or with a certain color. In addition or alternatively, theoutput device 126 is a display that displays information that a fault isdetected, the type of fault, and/or a location of the detected fault.

In addition or alternatively, the output device 126 may be configured tooutput any of the determined voltage levels and/or resistance values itdetermines for the stages. For example, the output device 126, such asone configured as a display, may be configured to output the voltagelevels and/or resistance values as a list or in a table, or in graphicalformat, such as a function of time and/or stages performed.

FIG. 2 shows a flow chart of an example method 200 of performing aninsulation resistance calculation process. The method 200 is describedwith reference to the fault monitoring device 104 of FIG. 1 . At block202, the controller 124 determines a state, of a plurality of states, inwhich to configure the secondary resistance circuit 116 for a currentstage, and configures the secondary resistance circuit 116 in thedetermined state, such as by configuring switches SW1, SW2 of theswitching circuit 116 in respective on/off states corresponding to thedetermined state. At block 204, in response to the secondary resistancecircuit 116 being configured in the current state, the controller 124determines a level of the high-side measurement voltage V_(MH) acrossthe high-side primary resistance R_(PH) measured by the high-sidevoltage measuring circuit 120, and determines a level of the low-sidemeasurement voltage V_(ML) across the low-side primary resistance R_(PL)measured the low-side voltage measuring circuit 122. Also, in variousembodiments, the method 200 may further include the high-side andlow-side voltage measuring circuits 120, 122 measuring the high-side andlow-side measurement voltages V_(MH), V_(ML) before the controller 124determines the levels of the high-side and low-side measurement voltagesV_(MH), V_(ML). Also, in various embodiments, the controller 124 maywait for a predetermined time period to allow transient voltages tosettle before the high-side and low-side voltage measuring circuits 120,122 measure the high-side and low-side measurement voltages V_(MH),V_(ML), and/or the controller 124 determines the levels of the high-sideand low-side measurement voltages V_(MH), V_(ML). At block 206, thecontroller 124 may determine or calculate a resistance value of ahigh-side insulation resistance R_(IH) and a resistance value of alow-side insulation resistance RI based on the levels of the high-sideand low-side measurement voltages V_(MH), V_(ML). In variousembodiments, the resistance values of the high-side and low-sideinsulation resistances R_(IH), R_(IL) may be based, or determined from,resistance values of a high-side parallel resistance connection of thehigh-side primary resistance R_(PH) and the high-side insulationresistance R_(IH) and a low-side parallel resistance connection of thelow-side primary resistance R_(PL) and the low-side insulationresistance R_(IL). Also, in various embodiments, the resistance valuesof the high-side and low-side parallel resistance connections may bebased on the voltage levels of the high-side and low-side measurementvoltages V_(MH), V_(ML) measured for the current stage and voltagelevels of the high-side and low-side measurement voltages V_(MH), V_(ML)measured for the directly prior stage. Additionally, in variousembodiments, the controller 124 may communicate with the output device126 to output the resistance values calculated at block 206. At block208, the controller 124 may determine whether to perform a next stage ofthe insulation monitoring process. If not, then the method 200 may end.If so, then the method 200 may proceed back to block 202, where thecontroller 124 performs the next stage.

FIG. 3 shows a flow chart of an example method 300 of performing thefirst fault monitoring process to detect whether a high-level fault ispresent in the high voltage bus 102. The method 300 is described withreference to the fault monitoring device 104 of FIG. 1 . At block 302,the controller 124 determines a state, of a plurality of states, inwhich to configure the secondary resistance circuit 116 for a currentstage, and configures the secondary resistance circuit 116 in thedetermined state, such as by configuring switches SW1, SW2 of theswitching circuit 116 in respective on/off states corresponding to thedetermined state. At block 304, in response to the secondary resistancecircuit 116 being configured in the current state, the controller 124determines a level of the high-side measurement voltage V_(MH) acrossthe high-side primary resistance R_(PH) measured by the high-sidevoltage measuring circuit 120, and determines a level of the low-sidemeasurement voltage V_(ML) across the low-side primary resistance R_(PL)measured the low-side voltage measuring circuit 122.

At block 306, the controller 124 determines at least one sampleresistance value corresponding to at least one of the high-side voltagerail 106 or the low-side voltage rail 108. An example sample resistancevalue corresponding to the high-side voltage rail 106 is, or is afunction of, a resistance value of the high-side parallel resistanceconnection R_(H) or the high-side insulation resistance R_(IH). Anexample sample resistance value corresponding to the low-side voltagerail 108 is, or is a function of, a resistance value of the low-sideparallel resistance connection R_(L) or the low-side insulationresistance R_(IL). For at least some embodiments, the controller 124calculates at least one of the high-side parallel resistance connectionR_(H), the high-side insulation resistance R_(IH), the low-side parallelresistance connection R_(L), or the low-side insulation resistanceR_(IL) according to equations (1)-(10) identified above.

At block 308, the controller 124 may compare the at least one sampleresistance value with at least one threshold. For example, thecontroller 124 may perform a first comparison that compares a firstsample resistance value corresponding to the high-side voltage rail 106with a first threshold, and/or may perform a second comparison thatcompares a second sample resistance value corresponding to the low-sidevoltage rail 108 with a second threshold. At block 310, the controller124 may determine whether a high-level rail fault is present based onthe at least one comparison. For example, if the first comparisonindicates that the first sample resistance value corresponding to thehigh-side voltage rail 106 is below the first threshold and/or if thesecond comparison indicates that the second sample resistance valuecorresponding to the low-side voltage rail 108 is below the secondthreshold, then the controller 124 may determine that a high-level railfault is present. Further, in some example embodiments, if thecontroller 124 determines that a high-level rail fault is present, thecontroller 124 may further determine a location of the high-level railfault. For example, if the first comparison indicates that high-levelrail fault is present, then the controller 124 may identify that thehigh-level rail fault is between the high-side voltage rail 106 andground GND. Additionally, if the second comparison indicates that thehigh-level rail fault is present, then the controller 124 may identifythat the high-level rail fault is between the low-side voltage rail 108and ground GND.

For at least some embodiments, the method 300 may further include ablock 312, where the controller 124, via the output device 126, outputsat least one output signal indicative of the fault result determined atblock 310. At block 314, the controller 314 may determine whether toperform a next stage. If so, then the method 300 may proceed back toblock 302. In some embodiments, the controller 314 determines to performa next stage if no high-level fault is detected at block 310. Otherwise,if a high-level fault is detected, then the method 300 may end.

FIG. 4 shows a flow chart of an example method 400 of performing thesecond fault monitoring process to detect whether a mid-level fault ispresent in the high voltage bus 102. The method 400 is described withreference to the fault monitoring device 104 of FIG. 1 . At block 402,the controller 124 determines a state, of a plurality of states, inwhich to configure the secondary resistance circuit 116 for a currentstage, and configures the secondary resistance circuit 116 in thedetermined state, such as by configuring switches SW1, SW2 of theswitching circuit 116 in respective on/off states corresponding to thedetermined state. At block 404, in response to the secondary resistancecircuit 116 being configured in the current state, the controller 124determines a level of the high-side measurement voltage V_(MH) acrossthe high-side primary resistance R_(PH) measured by the high-sidevoltage measuring circuit 120, and determines a level of the low-sidemeasurement voltage V_(ML) across the low-side primary resistance R_(PL)measured the low-side voltage measuring circuit 122.

At block 406, the controller 124 determines at least one sampleresistance value corresponding to at least one of the high-side voltagerail 106 or the low-side voltage rail 108. In particular embodiments,the at least one sample resistance value may include at least one of: adifference between a resistance value corresponding to the high-sidevoltage rail 106 and a resistance value corresponding to the low-sidevoltage rail 108, a moving average of resistance values corresponding toat least one of the high-side voltage rail 106 or the low-side voltagerail 108 determined from a number of previously performed stages, or arate of change of resistance values corresponding to at least one of thehigh-side voltage rail 106 or the low-side voltage rail 108 determinedfrom a number of previously performed stages.

At block 408, the controller 124 may compare the at least one sampleresistance value with at least one threshold. At block 410, thecontroller 124 may determine whether a mid-level rail fault is presentbased on the at least one comparison. For example, if the sampleresistance value is a difference, and the comparison indicates that thedifference is greater than a threshold, then the controller 124 maydetermine that a mid-level rail fault is present. As another example, ifthe sample resistance value is a moving average of resistance values,and the comparison indicates that the moving average is less than athreshold, then the controller 124 may determine that a mid-level railfault is present. In still another example, if the sample resistancevalue is a rate of change of resistance values, and the comparisonindicates that the rate of change is above a threshold, then thecontroller 124 may determine that a mid-level rail fault is present.Further, in some example embodiments, if the controller 124 determinesthat a mid-level rail fault is present, the controller 124 may furtherdetermine a location of the mid-level rail fault. For example, if thesample resistance value is a difference, then the controller 124 mayidentify which of the high-side and low-side insulation resistancesR_(IH), R_(IL) is lower, and in turn identify whether the mid-level railfault is between the high-side voltage rail 106 and ground GND orbetween the low-side voltage rail 108 and ground GND.

For at least some embodiments, the method 400 may further include ablock 412, where the controller 124, via the output device 126, outputsat least one output signal indicative of the fault result determined atblock 410. At block 414, the controller 124 may determine whether toperform a next stage. If so, then the method 400 may proceed back toblock 402. In some embodiments, the controller 414 determines to performa next stage if no mid-level fault is detected at block 410. Otherwise,if a mid-level fault is detected, then the method 400 may end.

FIG. 5 shows a flow chart of an example method 500 of performing thefirst and second fault monitoring processes in combination. The method500 is described with reference to the fault monitoring device 104 ofFIG. 1 . In the method 500, the fault monitoring device 104 may make afault determination for one of the first and second fault monitoringprocesses before determining a fault result for the other of the firstand second fault monitoring processes. The fault result that the faultmonitoring device 104 determines first is referred to as an initialfault result, and the fault that the fault monitoring device 104determines second is referred to as a subsequent fault result. Also, thefault monitoring process for which the initial fault result isdetermined is referred to as the initial fault monitoring process, andthe fault monitoring process for which the subsequent fault result isdetermined is referred to as the subsequent fault monitoring process. Insome embodiments of the method 500, the initial fault monitoring processis the first fault monitoring process, and the subsequent faultmonitoring process is the second fault monitoring process. In otherembodiments of the method 500, the initial fault monitoring process isthe second fault monitoring process, and the subsequent fault monitoringprocess is the first fault monitoring process.

In further detail, at block 502, the controller 124 determines a state,of a plurality of states, in which to configure the secondary resistancecircuit 116 for a current stage, and configures the secondary resistancecircuit 116 in the determined state, such as by configuring switchesSW1, SW2 of the switching circuit 116 in respective on/off statescorresponding to the determined state. At block 504, in response to thesecondary resistance circuit 116 being configured in the current state,the controller 124 determines a level of the high-side measurementvoltage V_(MH) across the high-side primary resistance R_(PH) measuredby the high-side voltage measuring circuit 120, and determines a levelof the low-side measurement voltage V_(ML) across the low-side primaryresistance R_(PL) measured the low-side voltage measuring circuit 122.

At block 506, the controller 124 may determine an initial fault resultfor an initial fault monitoring process. Additionally, in variousembodiments, the controller 124, via the output device 126, may outputthe initial fault result. For embodiments where the initial faultmonitoring process is the first fault monitoring process, the controller124 may determine the initial fault result by determining at least onesample resistance value, comparing the at least one sample resistancevalue with at least one threshold, and determining whether a high-levelrail fault is present based on the at least one comparison, such asdescribed above for blocks 306, 308, and 310 in the method 300 of FIG. 3. Additionally, for embodiments where the initial fault monitoringprocess is the second fault monitoring process, the controller 124 maydetermine the initial fault result by determining at least one sampleresistance value, comparing the at least one sample resistance valuewith at least one threshold, and determining whether a mid-level railfault is present based on the at least one comparison, such as describedabove for blocks 406, 408, and 410 in the method 400 of FIG. 4 .

At block 508, the controller 124 may determine whether to determine thesubsequent fault result. The determination may depend on which of thefault monitoring processes is initial fault monitoring process and theinitial fault result. Specifically, for embodiments where the initialfault monitoring process is the first fault monitoring process and theinitial fault result is that a high-level rail fault is present, thenthe controller 124 may determine to output that a high-level rail faultis detected, and stop further fault monitoring, including notdetermining the subsequent fault result. On the other hand, if theinitial fault result is that no high-level rail fault is present, thenthe controller 124 may determine to perform the subsequent, second faultmonitoring process to determine whether a mid-level rail fault ispresent. Accordingly, for this latter situation, the method 500 mayproceed to block 510 where the controller 124 determines the subsequentfault result, which is whether a mid-level fault is present. At block510, if the controller 124 has not already done so, the controller 124may determine at least one sample resistance value for the second faultmonitoring process, compare the at least one sample resistance valuewith at least one threshold, and determine whether a mid-level railfault is present based on the at least one comparison, such as describedwith reference to blocks 406, 408, 410 in the method 400 of FIG. 4 .

Additionally, for embodiments where the initial fault monitoring processis the second fault monitoring process and the initial fault result isthat a mid-level rail fault is not present, then the controller 124 maydetermine to not determine the subsequent fault result—i.e., whether ahigh-level rail fault is present—and proceed to block 512, where thecontroller 124 may determine whether to perform a next stage. On theother hand, if the initial fault result is that a mid-level rail faultis present, then the controller 124 may determine to perform thesubsequent, first fault monitoring process to determine whether ahigh-level rail fault is present. Accordingly, at block 510, if thecontroller 124 has not already done so, the controller 124 may determineat least one sample resistance value for the first fault monitoringprocess, compare the at least one sample resistance value with at leastone threshold, and determine whether a high-level rail fault is presentbased on the at least one comparison, such as described with referenceto blocks 306, 308, 310 in the method 300 of FIG. 3 .

The controller 512 may then proceed to block 512, and determine whetherto perform a next stage. If so, then the method 500 may proceed back toblock 502 and perform a next stage. If not, then the method 500 may end.

FIG. 6 shows a flow chart of an example method 600 of performing thethird fault monitoring process to detect whether an internal fault,internal to the voltage source 110, is present in the high voltage bus102. The method 600 is described with reference to the fault monitoringdevice 104 of FIG. 1 . At block 602, the controller 124 determines astate, of a plurality of states, in which to configure the secondaryresistance circuit 116 for a current stage, and configures the secondaryresistance circuit 116 in the determined state, such as by configuringswitches SW1, SW2 of the switching circuit 116 in respective on/offstates corresponding to the determined state.

At block 604, in response to the secondary resistance circuit 116 beingconfigured in the current state, the controller 124 determines a levelof the high-side measurement voltage V_(MH) across the high-side primaryresistance R_(PH) measured by the high-side voltage measuring circuit120 and/or a level of the low-side measurement voltage V_(ML) across thelow-side primary resistance R_(PL) measured the low-side voltagemeasuring circuit 122. At block 606, the controller 124 determines atleast one sample voltage level for the current stage that is, or is afunction of, at least one of the high-side measurement voltage V_(MH) orthe low-side measurement voltage V_(ML).

At block 608, the controller 124 determines at least one amount ofchange between the at least one sample voltage level for the currentstage and at least one sample voltage level determined from animmediately prior stage. At block 610, the controller 124 compares theat least one amount of change with at least one threshold. At block 612,the controller determines whether an internal fault is present based onthe comparison. For example, if an amount of change is above athreshold, then the controller 124 determines that no internal fault ispresent. If the amount of change is below a threshold, then thecontroller 124 determines that an internal fault is present. Also, insome embodiments, if the controller 124 determines that an internalfault is present, the controller 124 may further determine an internalfault location of the internal fault, such as a connection point betweentwo battery cells 112. As described, the controller 124 may determinethe internal fault location based on a first sample voltage levelcorresponding to the high-side voltage rail 106 and a second samplevoltage level corresponding to the low-side voltage rail 108, such as aratio between the first sample voltage level and the second samplevoltage level.

For at least some embodiments, the method 600 may further include ablock 614, where the controller 124, via the output device 126, outputsat least one output signal indicative of the fault result determined atblock 512. Also, in various embodiments, the controller 124 may output,via the output device 126, an internal fault location if it determinesone. At block 616, the controller 124 may determine whether to perform anext stage. If so, then the method 500 may proceed back to block 602. Insome embodiments, the controller 124 determines to perform a next stageif no internal fault is detected at block 612. Otherwise, if an internalfault is detected or the controller 124 otherwise determines not toperform a next stage, then the method 600 may end.

FIG. 7 shows a flow chart of an example method 700 of performing thethird fault monitoring process in combination with at least one of thefirst or second fault monitoring processes. The method 700 is describedwith reference to the fault monitoring device 104 of FIG. 1 . In themethod 700, the fault monitoring device 104 may make a faultdetermination for the third fault monitoring processes beforedetermining at least one fault result for at least one of the first orsecond fault monitoring processes. In the example method 700, whetherthe fault monitoring device 104 performs the first and/or second faultmonitoring processes may depend on a fault result of the thirdmonitoring process. Specifically, if the controller 124 determines thatan internal fault is present, then the controller 124 may not performany of the first and second fault monitoring processes. Alternatively,if the controller 124 determines that an internal fault is not present,then the controller 124 may perform at least one of the first or secondfault monitoring processes.

In further detail, at block 702, the controller 124 determines a state,of a plurality of states, in which to configure the secondary resistancecircuit 116 for a current stage, and configures the secondary resistancecircuit 116 in the determined state, such as by configuring switchesSW1, SW2 of the switching circuit 116 in respective on/off statescorresponding to the determined state. At block 704, the controller 124determines whether an internal fault is present in the high voltage bus102, such as by determining at least one level of the high-side andlow-side measurement voltages V_(MH), V_(ML), determining at least onesample voltage level for the current stage, determine at least oneamount of change between the at least one sample voltage level for thecurrent stage and at least one sample voltage level for a prior stage,comparing the at least one amount of with at least one threshold, anddetermining whether an internal fault is present based on the at leastone comparison, such as described with reference to blocks 604-612 ofthe method 600 of FIG. 6 . Also, in various embodiments, at block 704,the controller 124, such as via the output device 126, may output thefault result determined at block 704. Also, in some embodiments, if thecontroller 124 determines that an internal fault is present, thecontroller 124 may further determine an internal fault location of theinternal fault, such as a connection point between two battery cells112. As described, the controller 124 may determine the internal faultlocation based on a first sample voltage level corresponding to thehigh-side voltage rail 106 and a second sample voltage levelcorresponding to the low-side voltage rail 108, such as a ratio betweenthe first sample voltage level and the second sample voltage level.Also, the controller 124 may output the internal fault location, such asvia the output device 126, in various embodiments.

At block 706, the controller 124 may determine whether to determinewhether a high-level rail fault is present and/or a mid-level rail faultis present. Specifically, if the controller 124 determines that aninternal fault is present, then the controller 124 may determine not todetermine whether a high-level rail fault is present and whether amid-level rail fault is present, and the method 700 may end.Alternatively, if the controller 124 determines that an internal faultis not present, then the method 700 may proceed to block 708, where thecontroller 124 may determine at least one of whether a high-level railfault is present or a mid-level rail fault is present. For someembodiments, the controller 124 may determine only if a high-level railfault is present according to the first fault monitoring process. Forsuch embodiments, the controller 124 may perform blocks 304 to 310 ofthe method 300 as previously described to determine whether a high-levelrail fault is present. For other embodiments, the controller 124 maydetermine only if a mid-level rail fault is present according to thesecond fault monitoring process. For such embodiments, the controller124 may perform blocks 404 to 410 of the method 400, as previouslydescribed to determine whether a mid-level rail fault is present. Forstill other embodiments, the controller 124 may determine a combinationof whether the high-level and mid-level rail faults are present. Forthese embodiments, the controller 124 may determine an initial faultresult and optionally a subsequent fault result dependent on the initialfault result, such as by performing blocks 506, 508, 510, in combinationwith any of the blocks of FIGS. 3 and 4 , as previously described withreference to the method 500 of FIG. 5 . Also, in various embodiments, atblock 708, the controller 124, via the output device 126, may output onemore output signals indicating whether a high-level rail fault and/or amid-level rail fault is present. At block 710, the controller 124 maydetermine whether to perform a next stage. If so, then the method 700may proceed back to block 702. If not, then the method 700 may end.

While various embodiments have been described, it will be apparent tothose of ordinary skill in the art that many more embodiments andimplementations are possible. Accordingly, the embodiments describedherein are examples, not the only possible embodiments andimplementations.

The subject matter of the disclosure may also relate, among others, tothe following aspects:

Aspect 1. A fault monitoring device comprising:

a primary resistance circuit configured to connect to a high-sidevoltage rail and a low-side voltage rail of a high voltage bus of apower system;

a secondary resistance circuit configured to selectively connect to atleast one of the high-side voltage rail or the low-side voltage rail viaa switching circuit; and

a controller configured to:

-   -   selectively connect the secondary resistance circuit to the        high-side voltage rail and the low-side voltage rail over a        plurality of stages;    -   in response to the selective connection, measure a plurality of        sets of voltages over the plurality of stages; and    -   determine a plurality of pairs of resistance values for a        high-side insulation resistance and a low-side insulation        resistance of the power system, each pair of resistance values        based on a current set of measured voltages of a current stage        of the plurality of stages and a prior set of measured voltages        for a prior stage of the plurality of stages.        Aspect 2. The fault monitoring device of aspect 1, wherein the        controller is further configured to:

determine a plurality of pairs of parallel resistance values over theplurality of stages, each pair of parallel resistance values for: ahigh-side parallel resistance connection of a high-side resistance ofthe primary resistance circuit and the high-side insulation resistanceand a low-side parallel resistance connection of a low-side resistanceof the primary resistance circuit and the low-side insulationresistance; and

determine the plurality of pairs of insulation resistance values basedon the plurality of pairs of parallel resistance values.

Aspect 3. The fault monitoring device of aspects 1 or 2, wherein each ofthe plurality of stages corresponds to one of at least two differentstates of the secondary resistance circuit.Aspect 4. The fault monitoring device of aspect 3, wherein the at leasttwo different states comprises only two different states.Aspect 5. The fault monitoring device of aspect 3, wherein the at leasttwo different states comprises three or more different states.Aspect 6. The fault monitoring device of any of aspects 3-5, wherein thecontroller is configured to selectively connect the secondary resistancecircuit to the high-side voltage rail and the low-side voltage rail overa plurality of cycles, wherein for each cycle, each stage corresponds toa different one of the at least two different states.Aspect 7. The fault monitoring device of aspect 6, wherein thecontroller is configured to selectively connect the secondary resistancecircuit in each of the plurality of cycles according to a statesequence.Aspect 8. The fault monitoring device of any of aspects 1-7, wherein thesecondary resistance circuit comprises a high-side secondary resistanceand a low-side secondary resistance, wherein the controller is furtherconfigured to:

in a first stage of the plurality of stages, disconnect the high-sidesecondary resistance from the high-side voltage rail and the low-sidesecondary resistance from the low-side voltage rail;

in a second stage of the plurality of stages, disconnect the high-sidesecondary resistance from the high-side voltage rail and connect thelow-side secondary resistance to the low-side voltage rail;

in a third stage of the plurality of stages, connect the high-sidesecondary resistance to the high-side voltage rail and the low-sidesecondary resistance to the low-side voltage rail; and

in a fourth stage of the plurality of stages, connect the high-sidesecondary resistance to the high-side voltage rail and disconnect thelow-side secondary resistance from the low-side voltage rail.

Aspect 9. The fault monitoring device of any of aspects 1-8, wherein thecontroller is further configured to:

determine at least one sample resistance value associated with at leastone pair of resistance values of the plurality of pairs of resistancevalues for the high-side insulation resistance and the low-sideinsulation resistance;

compare the at least one sample resistance value with at least onethreshold; and

determine whether a fault is present in the power system based on thecomparison.

Aspect 10. The fault monitoring device of aspect 9, wherein the at leastone sample resistance value is, or is a function of, a differencebetween at least one high resistance value of the plurality of pairs ofresistance values that is for the high-side insulation resistance and aleast one low resistance value of the plurality of pairs of resistancevalues for the low-side insulation resistance.Aspect 11. The fault monitoring device of aspect 9, wherein the at leastone sample resistance value comprises a first sample resistance valuecomprising an average resistance value associated with the plurality ofpairs of resistance values, and a second sample resistance valueindicating a rate of change of resistance values associated with theplurality of pairs of resistance values.Aspect 12. A power system comprising:

a high voltage bus comprising:

-   -   a high-side voltage rail insulated from a chassis by a high-side        insulation resistance; and    -   a low-side voltage rail insulated from the chassis by a low-side        insulation resistance;

a fault monitoring device connected to the high voltage bus, the faultmonitoring device comprising a controller configured to:

-   -   determine a pair of resistance values corresponding to the        high-side insulation resistance and the low-side insulation        resistance;    -   determine whether a fault is present based on the pair of        resistance values; and    -   output, with an output device, a fault result indicating the        determination of whether the fault is present.        Aspect 13. The power system of aspect 12, wherein the fault        monitoring device further comprises a primary resistance circuit        and a secondary resistance circuit, and wherein the controller        is further configured to:

selectively connect the secondary resistance circuit to the high-sidevoltage rail and the low-side voltage rail over a plurality of stages;

in response to the selective connection, measure a plurality of sets ofvoltages over the plurality of stages; and

determine the pair of resistance values for the high-side insulationresistance and the low-side insulation resistance in response to theselective connection.

Aspect 14. The power system of aspects 12 or 13, wherein the controlleris configured to determine whether the fault is present by comparing afirst resistance value of the pair of resistance values with a firstthreshold and comparing a second resistance value of the pair ofresistance values with a second threshold within a single stage of aplurality of stages of a fault monitoring process.Aspect 15. The power system of aspects 12 or 13, wherein the controlleris configured to determine whether the fault is present by determining adifference between a first resistance value of the pair of resistancevalues and a second resistance value of the pair of resistance values.Aspect 16. The power system of aspects 12 or 13, wherein the controlleris further configured to:

determine a plurality of sample resistance values corresponding to thepair of resistance values over a plurality of stages;

determine at least one of: a moving average of the plurality of sampleresistance values or a rate of change of the plurality of sampleresistance values; and

determine whether the fault is present based on at least one of: themoving average being below a first threshold or the rate of change beingabove a second threshold.

Aspect 17. The power system of any of aspects 12 to 16, wherein thecontroller is further configured to identify a location of the fault inthe high voltage bus, the location being between the high-side voltagerail and the chassis or between the low-side voltage rail and thechassis.Aspect 18. The power system of any of aspects 12-17, wherein thecontroller, is configured to output, with the output device, the faultresult to indicate that the fault is a high-level rail fault determinedfor a first fault monitoring process, and to indicate that the fault isa mid-level rail fault determined for a second fault monitoring process.Aspect 19. A method comprising:

measuring, with a controller, a first pair of voltage levels across aprimary resistance circuit of an insulation monitoring device inresponse to a secondary resistance circuit of the insulation monitoringdevice being in a first state;

measuring, with the controller, a second pair of voltage levels acrossthe primary resistance circuit in response to the secondary resistancecircuit being in a second state different from the first state; and

determining, with the controller, a pair of resistance values for ahigh-side insulation resistance and a low-side insulation resistancebased on the first pair of voltage levels and the second pair of voltagelevels.

Aspect 20. The method of aspect 19, wherein the pair of resistancevalues comprises a first pair of resistance values, the method furthercomprising:

measuring, with the controller, a third pair of voltage levels acrossthe primary resistance circuit in response to the secondary resistancecircuit being in a third state different from the first state and thesecond state; and

determining, with the controller, a second pair of resistance values forthe high-side insulation resistance and the low-side insulationresistance based on the second pair of voltage levels and the third pairof voltage levels.

Aspect 21. A fault monitoring device comprising:

a primary resistance circuit configured to connect to a high-sidevoltage rail and a low-side voltage rail of a high voltage bus of apower system;

a secondary resistance circuit configured to selectively connect to atleast one of the high-side voltage rail or the low-side voltage rail viaa switching circuit; and

a controller configured to:

-   -   selectively connect the secondary resistance circuit to the        high-side voltage rail and the low-side voltage rail over a        plurality of stages;    -   in response to the selective connection, determine a plurality        of sample voltage levels corresponding to at least one of the        high-side voltage rail or the low-side voltage rail for the        plurality of stages, the plurality of sample voltage levels        comprising at least one current sample voltage level for a        current stage and at least one prior sample voltage level for a        prior stage; and    -   determine whether an internal fault is present in a voltage        source connected to the high-side voltage rail and the low-side        voltage rail based on the at least one current sample voltage        level and the at least one prior sample voltage level.        Aspect 22. The fault monitoring device of aspect 21, wherein the        controller is further configured to:

determine that the internal fault is present in response to at least oneamount of change between the at least one current sample voltage leveland the at least one prior sample voltage level not exceeding at leastone threshold; and

determine that the internal fault is not present in response to the atleast one amount of change exceeding the at least one threshold.

Aspect 23. The fault monitoring device of aspects 21 or 22, wherein theat least one current sample voltage level comprises a first currentsample voltage level corresponding to the high-side voltage rail and asecond current sample voltage level corresponding to the low-sidevoltage rail, and the at least one prior sample voltage level comprisesa first prior sample voltage level corresponding to the high-sidevoltage rail and a second prior sample voltage level corresponding tothe low-side voltage rail,

wherein the controller, in order to determine whether the internal faultis present, is configured to at least one of: compare the first currentsample voltage level and the first prior sample voltage level, orcompare the second current sample voltage level and the second priorsample voltage level.

Aspect 24. The fault monitoring device of aspect 23, wherein thecontroller is configured to both: compare the first current samplevoltage level and the first prior sample voltage level, and compare thesecond current sample voltage level and the second prior sample voltagelevel.Aspect 25. The fault monitoring device of aspect 24, wherein thecontroller is further configured to:

determine whether a rail fault is present in the high voltage bus inresponse to the controller determining that no internal fault ispresent.

Aspect 26. The fault monitoring device of any of aspects 21-25, whereinthe internal fault is between a location between two battery cells ofthe voltage source and a ground reference.Aspect 27. The fault monitoring device of any of aspects 21-26, whereineach of the plurality of stages corresponds to one of at least twodifferent states of the secondary resistance circuit.Aspect 28. The fault monitoring device of any of aspects 21-27, whereinthe controller is further configured to determine an internal faultlocation in response to determining that the internal fault is present.Aspect 29. The fault monitoring device of aspect 28, wherein thecontroller configured to determine the internal fault location based ona first sample voltage level corresponding to the high-side voltage railand a second sample voltage level corresponding to the low-side voltagerail.Aspect 30. A power system comprising:

a high voltage bus comprising:

-   -   a high-side voltage rail;    -   a low-side voltage rail; and    -   a voltage source connected to the high-side voltage rail and the        low-side voltage rail; and

a fault monitoring device connected to the high voltage bus, the faultmonitoring device comprising a controller configured to:

-   -   determine whether an internal fault is present between an        internal location of the voltage source and a chassis based on a        current sample voltage level determined from a current stage of        a fault monitoring process and a prior sample voltage level        determined from a prior stage of the fault monitoring process;        and    -   output, with an output device, a fault result indicating the        determination of whether the internal fault is present.        Aspect 31. The power system of aspect 30, wherein each of the        current sample voltage level and the prior sample voltage        correspond to at least one of the high-side voltage rail or the        low-side voltage rail.        Aspect 32. The power system of aspects 30 or 31, wherein the        controller is further configured to:

determine that the internal fault is present in response to an amount ofchange between the current sample voltage level and the prior samplevoltage level not exceeding a threshold.

Aspect 33. The power system of any of aspects 30-32, wherein thecontroller is further configured to:

determine that the internal fault is not present in response to anamount of change between the current sample voltage level and the priorsample voltage level exceeding a threshold.

Aspect 34. The power system of any of aspects 30-33, wherein thecontroller is further configured to:

determine whether a rail fault is present in the high voltage bus inresponse to the controller determining that no internal fault ispresent.

Aspect 35. The power system of aspect 34, wherein the controller isfurther configured to:

determine a pair of resistance values corresponding to a high-sideinsulation resistance and a low-side insulation resistance, the pair ofresistance values based on the current sample voltage level and theprior sample voltage level; and

determine whether the rail fault is present based on the pair ofresistance values.

Aspect 36. A fault detection method comprising:

switching, with a controller, a switching circuit into a first state ina first stage of a fault monitoring process;

determining, with the controller, a first sample voltage levelcorresponding to at least one of a high-side voltage rail or a low-sidevoltage rail with the switching circuit in the first state;

switching, with the controller, the switching circuit into a secondstate in a second stage of a fault monitoring process;

determining, with the controller, a second sample voltage levelcorresponding to the at least one of the high-side voltage rail or thelow-side voltage rail with the switching circuit in the second state;and

detecting, with the controller, whether an internal fault is present ina voltage source connected to the high-side voltage rail and thelow-side voltage rail based on the first sample voltage level and thesecond sample voltage level.

Aspect 37. The method of aspect 36, wherein detecting whether theinternal fault is present comprises:

determining, with the controller, whether an amount of change betweenthe first second sample voltage level and the second sample voltagelevel exceeds a threshold.

Aspect 38. The method of aspect 37, wherein detecting whether theinternal fault is present further comprises:

determining, with the controller, that the internal fault is present inresponse to the amount of change not exceeding a threshold.

Aspect 39. The method of any of aspects 36-38, further comprising:

determining, with the controller, whether a rail fault is present inresponse to detecting that no internal fault is present.

Aspect 40. The method of any of aspects 36-39, wherein the internalfault is between a location between two battery cells of the voltagesource and a ground reference of the high-side voltage rail and thelow-side voltage rail.

In addition to the features mentioned in each of the independent aspectsenumerated above, some examples may show, alone or in combination, theoptional features mentioned in the dependent aspects and/or as disclosedin the description above and shown in the figures.

What is claimed is:
 1. A fault monitoring device comprising: a primaryresistance circuit configured to connect to a high-side voltage rail anda low-side voltage rail of a high voltage bus of a power system; asecondary resistance circuit configured to selectively connect to atleast one of the high-side voltage rail or the low-side voltage rail viaa switching circuit; and a controller configured to: selectively connectthe secondary resistance circuit to the high-side voltage rail and thelow-side voltage rail over a plurality of stages; in response to theselective connection, determine a plurality of sample voltage levelscorresponding to at least one of the high-side voltage rail or thelow-side voltage rail for the plurality of stages, the plurality ofsample voltage levels comprising at least one current sample voltagelevel for a current stage and at least one prior sample voltage levelfor a prior stage; and determine whether an internal fault is present ina voltage source connected to the high-side voltage rail and thelow-side voltage rail based on the at least one current sample voltagelevel and the at least one prior sample voltage level.
 2. The faultmonitoring device of claim 1, wherein the controller is furtherconfigured to: determine that the internal fault is present in responseto at least one amount of change between the at least one current samplevoltage level and the at least one prior sample voltage level notexceeding at least one threshold; and determine that the internal faultis not present in response to the at least one amount of changeexceeding the at least one threshold.
 3. The fault monitoring device ofclaim 1, wherein the at least one current sample voltage level comprisesa first current sample voltage level corresponding to the high-sidevoltage rail and a second current sample voltage level corresponding tothe low-side voltage rail, and the at least one prior sample voltagelevel comprises a first prior sample voltage level corresponding to thehigh-side voltage rail and a second prior sample voltage levelcorresponding to the low-side voltage rail, wherein the controller, inorder to determine whether the internal fault is present, is configuredto at least one of: compare the first current sample voltage level andthe first prior sample voltage level, or compare the second currentsample voltage level and the second prior sample voltage level.
 4. Thefault monitoring device of claim 3, wherein the controller is configuredto both: compare the first current sample voltage level and the firstprior sample voltage level, and compare the second current samplevoltage level and the second prior sample voltage level.
 5. The faultmonitoring device of claim 4, wherein the controller is furtherconfigured to: determine whether a rail fault is present in the highvoltage bus in response to the controller determining that no internalfault is present.
 6. The fault monitoring device of claim 1, wherein theinternal fault is between a location between two battery cells of thevoltage source and a ground reference.
 7. The fault monitoring device ofclaim 1, wherein each of the plurality of stages corresponds to one ofat least two different states of the secondary resistance circuit. 8.The fault monitoring device of claim 1, wherein the controller isfurther configured to determine an internal fault location in responseto determining that the internal fault is present.
 9. The faultmonitoring device of claim 8, wherein the controller configured todetermine the internal fault location based on a first sample voltagelevel corresponding to the high-side voltage rail and a second samplevoltage level corresponding to the low-side voltage rail.
 10. A powersystem comprising: a high voltage bus comprising: a high-side voltagerail; a low-side voltage rail; and a voltage source connected to thehigh-side voltage rail and the low-side voltage rail; and a faultmonitoring device connected to the high voltage bus, the faultmonitoring device comprising a controller configured to: determinewhether an internal fault is present between an internal location of thevoltage source and a chassis based on a current sample voltage leveldetermined from a current stage of a fault monitoring process and aprior sample voltage level determined from a prior stage of the faultmonitoring process; and output, with an output device, a fault resultindicating the determination of whether the internal fault is present.11. The power system of claim 10, wherein each of the current samplevoltage level and the prior sample voltage correspond to at least one ofthe high-side voltage rail or the low-side voltage rail.
 12. The powersystem of claim 10, wherein the controller is further configured to:determine that the internal fault is present in response to an amount ofchange between the current sample voltage level and the prior samplevoltage level not exceeding a threshold.
 13. The power system of claim10, wherein the controller is further configured to: determine that theinternal fault is not present in response to an amount of change betweenthe current sample voltage level and the prior sample voltage levelexceeding a threshold.
 14. The power system of claim 10, wherein thecontroller is further configured to: determine whether a rail fault ispresent in the high voltage bus in response to the controllerdetermining that no internal fault is present.
 15. The power system ofclaim 14, wherein the controller is further configured to: determine apair of resistance values corresponding to a high-side insulationresistance and a low-side insulation resistance, the pair of resistancevalues based on the current sample voltage level and the prior samplevoltage level; and determine whether the rail fault is present based onthe pair of resistance values.
 16. A fault detection method comprising:switching, with a controller, a switching circuit into a first state ina first stage of a fault monitoring process; determining, with thecontroller, a first sample voltage level corresponding to at least oneof a high-side voltage rail or a low-side voltage rail with theswitching circuit in the first state; switching, with the controller,the switching circuit into a second state in a second stage of a faultmonitoring process; determining, with the controller, a second samplevoltage level corresponding to the at least one of the high-side voltagerail or the low-side voltage rail with the switching circuit in thesecond state; and detecting, with the controller, whether an internalfault is present in a voltage source connected to the high-side voltagerail and the low-side voltage rail based on the first sample voltagelevel and the second sample voltage level.
 17. The method of claim 16,wherein detecting whether the internal fault is present comprises:determining, with the controller, whether an amount of change betweenthe first second sample voltage level and the second sample voltagelevel exceeds a threshold.
 18. The method of claim 17, wherein detectingwhether the internal fault is present further comprises: determining,with the controller, that the internal fault is present in response tothe amount of change not exceeding a threshold.
 19. The method of claim16, further comprising: determining, with the controller, whether a railfault is present in response to detecting that no internal fault ispresent.
 20. The method of claim 16, wherein the internal fault isbetween a location between two battery cells of the voltage source and aground reference of the high-side voltage rail and the low-side voltagerail.